Aliens, Desirable and UndesirableAlien Flora of Britain by Stephen Troyte DunnReview by: R. Ll. P.The Irish Naturalist, Vol. 15, No. 2 (Feb., 1906), p. 28Published by: Irish Naturalists' Journal Ltd.Stable URL: http://www.jstor.org/stable/25522845 .

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28 The Irish Naturalist. February,

"of black slate in the south-westerni part of the present sheet were "separated out and distinguished as Coal-mneasures,' but, as will be "shown in the context, there is now strong reason to doubt whether "these beds should be regarded as Coal-measures."

In the chapter on the superficial deposits an interesting account is given of the discovery of "an ancient shore line of eEalier date than the glaciation of the district."

Part IL is occupied with a detailed description of the superficial de posits, and comprises 59 pages of closely printed matter of very great value.

Part III. gives in I8 pages an account of the "E Fconomic Geology' of

the area under the heads of Building Stone, Slates, Bricks, Silica Clay, Sand and Gravel, Road Materials, Water Supply, and Agricultural Geology. The latter includes useful notes on soils and subsoils, with a table showing their localities, nature, depths, and the petrological character of their contents.

There is a good index and an appendix containing a list of papers on the geology of the Cork district. The memoir is illustrated by several instructive figures in the text, and by six beautiful photographic plates by R. Welch.

T. F.

ALIENS, DESIRABLE AND UNDES1BABLE.

Alien Flora of B3ritaln. By STYapmN TROnYX DUNN, B.A., P.LS.

Pp. I6 + 208. London: West, Newman, and Co. io5. 'Price, 5s.

Before leaving England for Hong Kong in I903, Mr. Dunn issued'a

"Prelinminary List of the Alien Flora of Britain " This was a list only. Now, owing chiefly (so he tells us) to the industry of his wife, he has

been enabled to publish an interesting little book on the same subject, in which each of nearly a thousand species has appended to its name a

note varying in length from a few lines to half a page. These notes give the original home of each plant, and state or suggest its mode of origin in these islands, but they are a little disappointing in usually not

giving any indication of the British localities. "Trigonetla araica, Delile.-An Oriental weed, once recorded in England among grain aliens," does not, after all, convey much more information than was

given by the inclusion of the bare name in the "Preliminary List." But this does not much detract from the value of the book as a record

of- alien immigration and casual introduction.

Quite the most interesting feature of Mr. Dunn's book is the intro

duction, in which the questions of true nativity, of degrees of naturaliza

tion, of sources of introduction, and of the evidence to be emnployed in

fixing the standard of plants, are excellently dealt with. We would

like to see this essay read and taken to heart by every field botanist.

IL L4.. Pt

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