CANADA

Department of Northern Affairs and National Resources

FORESTRY BRANCH

THE TRANSLOCATION OF MINERALS

IN TREES

by

D. A. Fraser

Forest Research Division

Technical Note No. 47

1956

Published under the authority of

The Minister of Northern Affairs and National Resources

Ottawa, 1956

CONTENTS

PAGE

INTRODUCTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

RELATIVE ROLES OF XYLEM AND PHLOEM IN TRANSLOCATION. .. . . . . . . . . 6

ADVANTAGES AND METHODS OF USING RADIOISOTOPES IN TRANSLOCATION

STUDIES........ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

SUMMARY A D CONCLUSIONS...... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 14

REFERENCES. . . . . . . . . . . . . . . . . . . • . . . . . . . . . . . . . . . • . . . . . . . . . • . . . . . .. 15

78786-i!

(

The Translocation of Minerals in Trees!

Project P-377

by

D. A. Fraser�

INTRODUCTION

Green plants manufacture their own food from carbon dioxide and water through the process of photosynthesis. However, the presence of other elements in addition to carbon, hydrogen and· oxygen is essential both to the manufacturing process and to the healthy development of the plant. For almost a century there ,,,as a general as umption that only seven additional chemical elements­nitrogen, sulphur, potassium, calcium, magnesium, phosphorus and iron-were required. In the last decade, in addition to the ten elements which have been mentioned, several others have been found to be essential.

Carbon and oxygen are obtained chiefly from the air through leaves of the tree, and the remaining elements are absorbed from the soil by the roots and are translocated to other parts of the plant.

Trees require these essential elements for optimum growth, but the amounts and the time of their absorption from the soil depend on the species as well as on site conditions. Since silviculture is the art and science of cultivating forest crops, the forester must try to select treatments most appropriate to site con­ditions. It is true that empirical observations have greatly assisted the forester in assessing the quality of site as reflected in the volume of merchantable timber. The study of mineral requirements of tree species as well as the mineral trans­location within the tree will assist in site evaluation and recognition of diseases caused by mineral deficiencies. The present contribution reviews the literature pertaining to the translocation of minerals in trees and includes data from experiments in progress at the Petawawa Forest Experiment Station.

The treatment of physiology of trees apart from that of plant physiology in general may be justified by the special research methods necessitated by the size of trees. Usually instead of the regular laboratory techniques, those of experi­mental ecology, more suited to open-air conditions, have to be applied. How­ever, trees are still plants and therefore it is necessary to review translocation of minerals in plants before giving special consideration to trees.

The first phase in mineral transport involves the absorption of the element by the root, its movement across the cortex to the stele, and its subsequent upward translocation. Investigators have focused their attention on this first phase, and endeavoured to explain movement of minerals through recognized physical-chemical reactions that could result in a cellular transfer of minerals. Such processes include diffusion, ion exchange, Donnan equilibria and membrane potential. Although each of these mechanisms is important and could eventually in itself lead to the establishment of equilibria, yet one of the characteristics of ion transport in biological systems is its dependence on active metabolism, and

1 Invitation paper presented at the annual meeting of Canadian plant physiologists, October 3!, 1955, Ottawa, Ontario, Canada.

'Tree physiologist, Petawawa Forest Experiment Station, Chalk River, Ontario.

5

on the fact that the living cell is not in equilibrium with the environment (Stein­bach, 1951). Concerning this aspect, the studies of Epstein and Hendricks (1955) on ion transport in the roots of higher plants have shown that ions move freely into and out of an "outer" space of the roots. This takes place by diffusion and exchange, independently of the simultaneous active transport of the same ions which results in their transfer into an "inner" space where they are no longer exchangeable with the same or other ions. Epstein (personal communi­cation) considers that these inner and outer spaces in the root do not represent distinct tissues but rather parts of cells. The outer space is intracellular and is identified with the cytoplasm. Since entry into and exit from this space is by diffusion, it develops that the outer membrane of cytoplasm is quite permeable to ions, and therefore is not the membrane which operates the active metabolic mechanism of ion transport. These exchange and diffusion processes are reversible, non-selective, non-metabolic, and come to equilibrium approximately within an hour after immersion of the roots in a new solution. Kramer and Wiebe (1954) noted that the meristematic region of the roots accumulates large amounts of minerals but very little is translocated from it to other parts of the plant. They concluded that most of the minerals translocated out of the roots are absorbed by the root-hair zone, or region of differentiation.

RELATIVE ROLES OF XYLEM AND PHLOEM IN TRANSLOCATION

There has been conflicting evidence as to the relative roles played by xylem and phloem in the up\vard translocation of minerals. Some physiologists (Curtis and Clark, 1950) do not consider any difference in the mechanisms of transport of inorganic and organic substances, except that the latter are more usually transported and required by different parts of the plant in larger amounts. Curtis (1925) found removal of the bark (ringing) would interfere with the upward transfer of solutes. In his experiments, divided stem were used, \\'here water was supplied to the top by one set of roots and nitrogen by another set. Results indicated that if the roots supplied with nitrogen were connected to the tops by xylem only, there was little transfer of nitrogen, while if they were connected by phloem only, considerable transfer occurred. Diffusion alone could not account for this rapid movement, and Curtis thought that protoplas­mic streaming within the cells may have been a factor.

Evidence showing that there is no direct relation between water absorption and salt absorption was given by Muenscher (1922) in his work on the effect of transpiration on· ab orption of salts by plants. Mason, Maskell, and PhiJIis (1936) verified this work and mentioned that oxygen deficiency, induced locally, could reduce transport, but not always, since the transpiration stream may carry enough oxygen.

It is considered that minerals can move upward through the phloem, especially if the leaves have not expanded. There are conflicting observations on the importance of the phloem in upward transport from roots to leaves. Stout and Hoaglund (1939), using radioactive tracers, found that when the xylem and phloem were separated, upward transport took place almost entirely in the xylem. Curtis and Clark (1950) compared these negative results for phloem transport with the positive results of Biddulph and Markle (1944). The latter authors allowed their plants to stand overnight to recover from the shock of having the phloem separated from the xylem and they found phosphorus movement upward and downward through the phloem.

It is probable that either phloem or xylem alone can transport the required minerals. Curtis and Clark (1950) summarize mineral transport thus: "that the xylem is concerned with mineral transport more (1) in herbaceous plants than in woody; (2) in those plants showing active root pressure than in those without root pressure; (3) near the base of the plant than in the

6

upper part; (4) when there is an excess of the particular element than when it is deficient; (5) more, especially of nitrogen, when the roots have a low car­bohydrate content than when it is high; (6) possibly more of the salts like calcium, zinc, and iron, that are not greatly accumulated in living cells; and (7) possibly more of the elements that are less likely to be carried in combination with organic molecules" .

ADVANTAGES AND METHODS OF USING RADIOISOTOPES IN

TRANSLOCATION STUDIES

In older methods of research on translocation, dyes )vere used which were injected into the tree, and could be detected visually when the tree was cut down. This technique was applicable more to the study of water movement than to that of translocation of minerals. Other workers used poisons and they hoped that the movement of a poison would be accompanied by external symptoms such as a change in appearance of the foliage. It was not until the radioisotope became available that investigators could tag an element which would emit detectable radiation, and thus permit its observation without ·killing the tree.

There are several kinds of radiations. According to the present atomic theory, the atom is made of a nucleus about which revolve particles known as electrons. The mass of the atom is found primarily in the nucleus which, for present purposes, consists of protons having a positive charge and neutrons having no charge. The neutrons affect the mass but not the chemical properties of the element, and atoms which vary in nuclear mass but have the same chemical behaviour are called isotopes. When these emit radiations which may be detected by various types of counters, they are referred to as radioisotopes. Radiations are of three types depending on the characteristics of the radioisotope.

(1) Alpha rays: are helium nuclei or alpha particles which have a rela-

(2) Beta rays:

tively large mass compared with electrons but possess a very limited penetration power.

are negative electrons emitted from atomic nuclei; these have a limited penetration power but give good resolution in autoradiography.

(3) Gamma rays: are electromagnetic radiation similar to X-rays; these are very penetrating and may be easily detected by external monitoring.

The last two types of radiations are most suitable for biological research and problems pertaining to forestry.

Radioisotopes are useful in biological research in several ways. They are very good analytical tools which increase the sensitivity and ease of analysis available through conventional methods. They also permit the measurement of ion fluxes in a given direction even when there is no net flux of that ion, or when the net flux is in the opposite direction. In tree investigations the use of the radioisotope permits detection within the tree by external monitoring. This has certain advanLages over older methods since the tree does not have to be sacrificed in order to determine the translocation of the element within the tree.

The major minerals required by trees, as indeed by plants in general, include, in addition to carbon, hydrogen and oxygen, thirteen mineral elements-potas­sium, calcium, magnesium, nitrogen, phosphorus, sulphur, iron, manganese, zinc, copper, molybdenum, boron and chlorine. Of these, only nitrogen and boron have no radioisotopes suitable for tracers. Several other elements such as sodium, cobalt, and rubidium, although not known to be essential, posse s suitable isotopes and are of physiological interest. Growing plants in nutrient

7

solutions and determining the mineral content of plant tissues by ashing are two important methods for determining mineral requirements and plant reactions to deficiencies.

Biddulph (1953) considers that reactions involving the precipitation of certain mineral nutrients in the xylem extremities may be respon ible for the failure of delivery of some minerals to the leaf mesophyll. Such elements as zinc and iron form insoluble precipitates with phosphorus. Rediske (1950) has shown deposition of radioiron in the veins of bean leaves by creating particular pH and phosphorus levels within the nutrient solution, namely pH 7·0, 0·0001 M phosphorus and 1 ppm iron. At higher phosphorus levels, iron was largely precipitated in the roots and little entered the aerial parts. The nutrient conditions effecting this were pH 7·0, 0·001 M phosphorus and 1 ppm iron. With nutrient solution at pH 4·00 but other conditions as first mentioned, the leaves were a healthy green indicating a normal upply of iron.

Certain elements have a characteristic distribution in plants. Some, like phosphorus, are freely mobile within the plant so that a supply ab orbed early in the season may be utilized elsewhere in the plant when none is available to the roots. Sulphur behaves similarly. Calcium is different from phosphorus and sulphur in that it i usually deposited and the part which is absorbed earlier is of no value for later new growth. Iron is like calcium, although a very pro­nounced absorption in the roots may be released later to newly growing part .

Movement of minerals from leaves to other parts of the plant may be followed by tracing a radioisotope which was applied to a leaf. The conditions which control movement of minerals from mature leaves vary with the element studied. Phosphorus and sulphur move out freely and are little affected by the nutrient conditions of the plant prior to, or during, the experimental period. Iron, calcium, and zinc ordinarily move from the leaf in very small amounts and can be further immobilized by a high concentration of pho phorus in the tissues of plants grown at pH 7·0 or above.

Biddulph (1951) introduced water made with tritium in which phosphorus32 was dissolved, directly into the leaves, and then isolated the two radioactive components in the stem and root tissues below the point of introduction. No marked movement of the water took place in the phloem tis ue of the stem, but the phosphorus32 introduced with the tritiated water moved freely. He considers the mechanism of translocation of minerals in the phloem not simple diffusion ince it is activated in some manner to attain speeds approaching three feet

per hour.

The roots require minerals for their growth and consequently compete for elements which are to be translocated to the aerial parts. Biddulph (1953) investigated this aspect of retention and transport by the root for phosphorus and rubidium. This study extended over a 24-hour period so that diurnal variations in both retention and translocation were evident. The translocation cycle wa found to be light-sensitive as well as to possess an inherent cyclic phase independent of light.

Bu gen and Munch (1929) state that trees obtain their supply of minerals at different periods in the growing season. Larch and pine take up most of their potassium from mid-June to mid-September, while spruce supplies itself with this element from mid-May to mid-June. The larch shows light absorption of phosphorus in summer and a great absorption in autumn, while pine absorbs phosphorus exclusively in late summer, and spruce only in the spring and early ummer. Ramann and Bauer (1912) showed a corre ponding behaviour for

nitrogen in these species and considered it a reason for the success of mixedwoods as compared to pure stands.

Broadleaved trees have a maximum absorption of minerals in early summer except for calcium, which is absorbed to a greater extent in late summer. Since the spring shoots and leaves are formed almost entirely from reserve materials, the older parts of the tree are to a great extent impoverished in mineral matter by the formation of shoots.

Ramann (1912) , in an investigation of mineral content of deciduous trees in daytime and night, found that the calcium content rises at night and falls during the day. He concluded from this that calcium takes part in the transport of a similates from the leaves during the formation of organic substances in the day and a replacement of the calcium takes place at night. No migrations of other mineral substances were found leading to a noticeable difference in the composition of the ash in the daytime and at night.

Biddulph (1953) considers that a re-export of minerals from leaves is required since the transpiration stream will continually make a supply of minerals available at the end of the veins in the leaves. These minerals would be lost to other parts of the plant for future growth if the excess were not transported back into the plant body. Phosphorus moving out of the leaf downwards in the phloem, if not incorporated in living tissue, may move up again through the xylem.

Another pha e of the re-export of minerals from leaf tissue often takes place before death or abscission. Deleano and Andreescu (1932) investigated changes in amounts of certain minerals in willow (Salix jmgilis), as it occurs throughout the season. They found little change in calcium content before leaf fall. Iron, manganese, and silicon behaved similarly. However, magnesium, potassium, phosphorus, chlorine, and nitrogen were mobile and more than half was removed before leaf fall. ome of this export may have resulted from leaching by rain or dew.

In a study of movement of radioisotopes in yellow birch (Betula lutea Michx. f.) and white pine (Pinus strobus L.) , Fraser and Mawson (1953) developed a special portable scintillation counter for measuring radioisotope movement along tree trunks. These investigator had previously u ed a portable health monitor (a Geiger-Mueller counter) to detect radiation in field experiments (Fraser, 1950) . Although this instrument was quite sensitive, it possessed numerous disadvantages. The instrument was rather heavy and awkward to carry, and the short lead to the probe made it difficult to obtain readings higher up in the tree. In addition, the probe had no attachment to ensure uniformity of position in repeated observations at different levels. Accordingly an instru­ment was constructed incorporating the desired modifications (Figure 1).

In this apparatus the batteries are encased in a metal box which fits into a pack ack provIded with houlder straps. The counter, with a visual indicator for recording activity, is equipped with a strap which holds it at chest level. On the right side of the counter are two sockets, one for the insertion of the lead to a scintillation probe, the other for a Geiger-Mueller probe.

By the scintillation method, ionizing radiation is counted by photoelectric measurement of the fluorescent light pulses emitted by certain organic substances. Anthracene is the organic substance used in this probe. A p.ollimator, with its outer face so indented a to fit securely against the tree trunk, was fitted over the end of the probe. A notched projection is attached to the collimator so that when the probe is in use, the notch may be slipped around the projecting end of a nail inserted into the tree trunk. The probe is then rotated to a hori­zontal position, thus ensuring a uniform position of the scintillation probe for repeated observations.

Movements of rubidium86 and calcium45 were followed with this newly­developed portable scintillation counter. The isotopes were introduced into soil or nutrient solutions containing branch roots, and also directly into the tree trunks. For the latter work, rubidium86 carbonate in a solution of five per cent

9

FIGURE 1. Monitoring movement of rubidium86 in yellow birch with portable scintil­

lation counter. The operator is holding the probe in his left hand, with

the counter strapped to his waist.

potassium chloride was placed in a water-tight trough constructed around part of the tree trunk. A i-inch chisel with its face parallel to the vertical axis was used to make an under-water incision to a depth of one inch. U e of the potas­sium chloride facilitated the entrance and movement of the isotope in the trans­location stream. The maximum rate of upward movement of the rubidium86 in the xylem of yellow birch approximated one foot per minute along a narrow channel spiralling upward (usually dextrally) from the point where the isotope was first introduced. Movement in decadent yellow birch was very slow with an: apparent increa e of permeability of the bark tissue as indicated by lateral diffusion of the isotope. In October no upward movement was discerned in healthy trees but rather a downward translocation in the phloem which may have been associated with the removal of certain minerals from the senescent leaves. Samples of phloem and xylem ,vere removed with an increment borer for radioactive assay, to facilitate the interpretation of the external monitoring observations.

10

Calcium45 injected into the white pine trunk had a localized distribution similar to that of the rubidium86 in yellow birch. In the white pine trunk the isotope moved upwards from the point of infection, along a relatively narrow channel. Only two branches, both within six feet of the ground, were found to contain appreciable activity. Monitoring records on August 22, six weeks after injection, indicated an accumulation of calcium in the main trunk at a point where the upper active branch had its origin. From this position in the trunk, most of the calcium was carried out into the branch. The isotope was not evenly distributed throughout the branch, as in any given whorl of twigs some were much more active than others.

The internal distribution of the calcium was investigated by autoradiographs. In this technique (Belanger and Leblond, 1946) sections of tissue are coated with a photographic emulsion and left for different periods of exposure ranging from a few hours to several weeks depending on the degree of localization of the radioisotope and consequent inten ity of radiation to which the photographic emulsion in contact with the section is exposed. The autoradiographs of ections of the stem (Figure 2) showed activity in the sieve cells of the phloem in the white pine.

During September some of the calcium45 concentrations had materialized into visible crystals. Figure 3 shows a cross section of crystals in the phloem cells. By focusing up on the photographic emulsion covering the section of these cells, the dark dots (Figure 4) represent exposure of the photographic emulsion indicating that these cells contain calcium45•

Presence of calcium45 was also noted in the buds of yellow birch. Figure 5a presents photographs of the buds, whereas Figure 5b show autoradiographs of the same buds indicating the presence of calcium45 in the peripheral parts of these buds.

Moreland (1950) introduced roots of loblolly pine into jars containing phosphorus32 solution and noted a maximum translocation rate of more than four feet per hour.

Yli-Vaakuri (1954) in Finland showed that movement of phosphorus32 would take place from tree to tree and also between trees and stumps through natural root grafts.

Kuntz and Riker (1955) in Wisconsin studied more extensively the use of radioisotopes for ascertaining the role of root grafts in the translocation of minerals between trees. Their experiments with iodine131 and rubidium86 included the insertion of cut branches or roots into a bottle containing a radio­active solution, or injection of a solution from a cone or trough similar to the technique used by Fraser and Mawson (1953).

The usual rate of upward movement of the isotope in the translocation stream of oaks in full sunlight and with low relative humidity was between It and 3 feet per minute. A limited downward movement into the roots was noticed. Greater movement occurred in roots naturally grafted onto those of other trees. Radioactivity was detected within 20 minutes in most branches, twigs, and leaves of pin oak (Quercus ellipsoidalis E. J. Hill) 35 feet high. Radio­activity appeared only in narrow vertical streaks which originated at the chisel cuts, and in certain branches of the bur oak (Quercus macro carp a Michx.) . The diffuse movement of the isotopes throughout trunks and the crown of the northern pin oak was quite different from the limited linear flow in the trunk and certain branches of the bur oak. In this respect the bur oak behaved like the yellow birch and white pine in the experiments by Fraser and Mawson (1953) . Movement of the isotopes was reduced by very low light intensities, free moisture on the leaves, and absence of functional leaves. Little movement occurred during the dormant period. When dominant and suppressed trees were con­nected by root grafts, isotopes moved both ways but most commonly from the

11

FIGURE 2. Autoradiograph of longitudinal section of wood and bark of white pine stem showing localization of calcium" in phloem.

FIGURE 3. Crystals in phloem of white pine (dark rectangular shapes in centre of picture).

12

FIGURE 4. Autoradiograph of section shown in Figure 3. The black areas indicate the presence

of calcium" in the crystals.

FIGURE 5a. Longitudinal sections of yellow birch buds in natura.

FIGURE 5b. Autoradiograph of yellow birch buds shown in Figure 5a, indicating presence of calcium".

dominant to the suppressed tree. The failure of the isotopes to move in trees with oak wilt led to the discovery that xylem vessels in the aerial parts were plugged with tyloses and gum.

Tukey et al (1955) applied cotton gauze which had been dipped into solutions of potassium42 carbonate and ortho phosphoric32 acid, around branches of apple trees and peach trees. Within 24 hours of application during February and March, even with freezing temperatures, radioactivity was detected within the branches 18 to 24 inches above and below the points of application. Similar applications made just. as the buds were beginning to swell indicated that the activity moved through the bark, up through the branches and concentrated near the buds, presumably to be available for the flush of new growth. The work of these investigators indicated that nitrogen, phosphorus, potassium, and rubidium applied to leaves are transported both acropetally and basipetally. Calcium, strontium, and barium do not move from the absorbing plant part, and basipetal transport is negligible.

Ferrel and Hubert ( 1952), in a study of the pole blight condition in western white pine (Pine monticola Dougl.) in Idaho, found that phosphorus and calcium had unusual distribution in pole-blighted trees. In diseased trees, phosphorus content was found to be higher than in normal trees and the calcium content lower. This greater accumulation of phosphorus was considered related to the more rapid radioisotope movement up the pole-blighted trees and associated with the greater transpiration. Farrar ( 1953) also noted greater movement of phosphorus32 into older needles of red pine as compared with newly formed needles. Tamm ( 1951) reported that the composition of rain water samples collected beneath trees, as compared with samples from an open field, contained considerable amounts of calcium, potassium and sodium, together with smaller amounts of nitrogen and phosphorus.

13

SUMMARY AND CONCLUSIONS

It appears that either xylem or phloem may transport upwards the elements required, but that phloem may be more important for mineral translocation in trees. This seemed evident in the localization of calcium45 in the phloem sieve cells of white pine. The unusual distribution of calcium in pole-blighted western white pine along with a very high phosphorus content parallels the experiments where radioactive iron ,vas deposited in the roots or leaf veins and was un­available to the leaf mesophyll when nutrient conditions had a high pH and an abundance of phosphorus. The important influence of the soil solution pH on the uptake and final distribution of iron thus indicates the effect of the environment on the translocation of minerals within a plant. The use of the radioisotope has greatly facilitated the study of mineral movement in trees and led to the development of a new portable scintillation counter especially suited for tree studies.

The linear flow of minerals in white pine, yellow birch and bur oak was in contrast to the diffuse movement in northern pin oak. Minerals moved between trees through natural root grafts. The failure of isotopes to move in trees with oak wilt led to the di covery that xylem vessels in the aerial parts were plugged with tyloses and gum.

The availability for tree growth of minerals in the soil and their subsequent uninterrupted translocation to all parts of the growing tree are essential for maximum size. Information on the variability of species as to their ability to utilize minerals, both at different times of the year and to different extents, should assist in assessing optimum silvicultural methods for various sites and species.

Acknowledgments

The author wishes to thank Dr. Erika Gaertner for assistance in monitoring radioactive trees. Dr. C. A. Mawson and N. Vincent, Atomic Energy of Canada Limited, Chalk River, Ontario, provided invaluable assistance in the preparation of the isotopes and au toradiographs. Colleagues at the Petawawa Forest Experiment Station provided constructive criticism in the preparation of the manuscript. Photograph for Figure 1 was taken by Dr. Gaertner; those for Figures 2, 3 and 4 with the assistance of D. C. Anderson, Forest Biology Laboratory, Sault Ste. Marie, Ontal:io.

14

REFERENCES

BELANGER, H. F. and C. P. LEBLOND. 1946. A method for locating radioactive elements by covering histological sections with a photographic emulsion. Endocrinology, 39:8-13.

BIDDULPH, O. 1951. The translocation of minerals in plants. In Mineral nutrition of plants, Ed. E. Truog. Univ. Wisconsin Press, Madison, 261-275.

BIDDULPH, O. 1953. Translocation of minerals in plants. In Use of isotopes in plant and animal research. Kansas Agric. Expt. Sta. Rept. 4:48-51

BIDDULPH, 0., and J. MARKLE. 1944. Translocation of radiophosphorus in the phloem of cotton. Amer. J. Bot. 31 :65-70.

BUSGEN, M., and E. MUNCH. 1929. The structure and life of forest trees. Eng. Trans!. by T. Thomson. Chapman and Hall, Ltd. London.

CURTIS, O. F. 1925. Studies on the tissues concerned in the transfer of solutes in plants. The effect on the upward transfer of solutes of cutting the xylem as compared with that of cutting the phloem. Ann. Bot., Lond. 39:573-585.

CURTIS, O. F., and D. G. CLARK. 1950. An introduction to plant physiology. McGraw Hill Book Co., N.Y.

DELEANO, N. T., and M. 1. ANDREESCU. 1932. Beitriige zum Studium der Rolle und Wirkung­sweise der Mineral-und organischen Stoffe in Pflanzenleben. 1. Der Quantitative StotTwechsel der Mineral-und organischen Substanzen in den Salix fragilis-Blattern wahrend ihrer Entwicklung. Beitr. BioI. Pflanz. 19:249-286.

EpS'fEIN, E., and S. B. HENDRICKS. 1955. Uptake and transport of mineral nutrients in plant roots. A/Conf. 8/p 112, Geneva.

FARRAR, J. L. 1953. Distribution of radiophosphorus in red pine seedlings. Canada, Dept. Resources and Development, Forestry Branch, Silv. Leaf!. No. 78.

FERREL, W. K., and E. E. HUBERT. 1952. The use of radioisotopes in forest tree research. Idaho Forester, 34:42-45.,

FRASER, D. A. 1950. Movement of radioactive calcium in white pine and yellow birch. Ann. Tech. Report, Forest Insect Lab., Sault Ste. Marie, Ontario. (Unpublished.)

FRASER, D. A., and C. A. MAWSON. 1953. Movement of radioactive isotopes in yellow birch and white pine as detected with a portable scintillation counter. Canad. J. Bot. 31 :324-333.

KRAMER, P. J. and H. H. WIEBE. 1954. Mineral absorption through various regions of roots. 8th Int. Bot. Congo Paris. Sec. 11 :82-83.

KUNTZ, J. E., and A. J. RIKER. 1955. The use of radioactive isotopes to ascertain the role of root grafting in the translocation of water, nutrients and disease-inducing organisms among forest trees. A/Con£' 8/P /105. Geneva.

MASON, T. G., E. J. MASKELL, and E. PHILLIS. 1936. Further studies in the cotton plant. III-Concerning the independence of solutes movement in the phloem. Ann. Bot., Lond. 50:23-58.

MORELAND, D. E. 1950. A study of the translocation of radioactive phosphorus in loblolly pine (Pinu8 taeda L.). Jour. Eli�ha Mitchell Sci. Soc. 66:175-181.

MUENSCHER, W. C. 1922. The effect of transpiration on the absorption of salts by plants. Amer. J. Bot. 9:311-329.

.

RAMANN, E. 1912. Mineralstoffgehalt von Baumblattern zur Tages und zur Nachtweit. Jahr. f. Wiss. Bot. 50:84-91.

RAMANN, E., and H. BAUER. 1921. Trochensubstanz Stickstoff und Mineralstoffe von Bau­marten wahrend einer Vegetationsperiode. Jahr. f. Wiss. Bot. 50:67-83.

REDISKE, J. H. 1950. The translocation of radioiron in the bean plant. Thesis, State College of Washington.

15

STEDIBACH, H. B. 1951. Permeability. In Ann. Rev. Plant Physiol. 2:323-342.

STOUT, P. R. and D. R. HOAGLUND. 1939. Upward and lateral movement of salt in certain plants as indicated by radioisotopes of potassium, sodium and phosphorus absorbed by the roots. Amer. J. Bot. 26 :320-324.

TMDf, C. O. 1951. Removal of plant nutrients from tree crowns by rain. Physiol. Plant., Copenhagen 4:184-188.

TUKEY, H. B., S. H. WITTWER, F. G. TEUBNER, and W. G. LO:-iG. 1955. Utilization of radio­isotopes in resolving the effectiveness of foliar absorption of plant nutrients. A/Conf. 8/P /106. Geneva.

YLI-V AAKURI, PAAVO, 1953. Untersuchungen liber organische Wurzelverbindungen zwischen Baumen in Kiefernbestanden. Acta Forestalia Fennica 60:1-117.

EDMOND CL OUTI E R, C.M.G., O.A., D.S.P.

QU E EN'S P RINT E R AND C ONT R OLL E R OF STATI ON E RY

OTTAWA, 1956

16