The Red Colouring of Arctic Plants. 83

MYCORHIZA AND ITS SIGNIFICANCE.

ln connection with Stahl's recent important work' on thesignificance of that intimate association of certain fungi with theroots of many plants known as "Mycorhiza" (now knownto be a phenomenon affecting probably considerably more than halfthe species of the higher plants), and his theory that Mycorhiza iscorrelated with a difficulty of obtaining nutritive salts, with feebletranspiration, and with poverty or absence of starch formation in theleaves, it is of great interest to note, as Dr. Wulff puints out (1) that aconsiderable number of arctic plants have Mycorhiza, (2) that of 16species collected and investigated by him all shew marked sugar-reaction,' and absence or poverty of starch, and (3) as has beenalready shown, arctic plants have a very feeble transpirationcurrent. Though the exact relations of these series of facts is notwholly clear, their causal connexion certainly seems indicated.

Thus the Mycorhiza-symbiosis would fall, at least so far as thenature of the soil in which the affected roots live is concerned, intotwo very distinct classes of cases; first, those in which the soil islargely composed of humus or leaf-mould, comparatively poor ininorganic salts, among which may be mentioned the beech and thehazel of our own woodlands ; and secondly those in which the soilis quite destitute of humus and while possibly rich in inorganicsalts cannot supply these freely to the plant owing to the lack of anadequate transpiration-current.

THE RED COLOURING OF ARCTIC PLANTS.

The extraordinary purity and brightness of the colours of manyAlpine flowers (and the same is true of Arctic ones) is well known.The vivid colouring often extends to the whole subaerial part of theplant, the leaves and stems shewing a deep red or purple whichoften masks the ordinary chlorophyll green. This is due to thepresence of soluble red, purple or blue pigments in the cell-sap ofvarious living cells ot the leaf and stem, very rarely [Eriophovumaiigiistifoliim vav. tniie) to colouration of cell-walls; to these pigmentsthe collective name Anthocyanin has been given. Dr. Wulff findsthat the presence of this pigment is an almost universal characteristic of Arctic plants. In a very interesting paper published three

' Dr. WulfF took precautions against coiifouuding siigai-reactiou with taimiii-reactiou.

' Der vSiuu der Mycorliizeiibilduug. Jalirb. f. wiss. Botaiiik,xxxiv., 1900.