296 THE JOURiN^AL OF BOTAIfT 



(1) Bark-lichen, (2) Earth-lichen, and (8) Eock-lichen. Under 

 these headings, which represent the substrata, lie describes the 

 occurrence of the lichens, the influence of the varj^ing tj-pes of tree, 

 soil, or stone, and the effect even in Iceland of variations of climates. 

 Dr. Galliz^e considers that severe cold affects the grovvth of lichens 

 adversely. This has not been altogether the expeiience of lichenolo- 

 gists in other regions. Tlie boulders in Antarctic areas were found 

 to be completely clothed with lichen vegetation ; a great point in 

 their favourable development was the absence of competition with 

 other plants, an advantage which we are told is shared by the rock- 

 lichens of Iceland. 



In a previous part of the Botany of Iceland, Hesselbo gave much 

 attention to the influence of hot springs on the moss vegetation in 

 their neighbourhood (see Journ. I3ot. 1918, p. 278). Some account of 

 the lichens (if there be any) growing in these areas would have been 

 of extreme interest, and it is to be regretted that the opportunity to 

 discuss such an important ecological question has been missed. 



As regards vertical distribution, the author concludes from his 

 observations that lichens are least abundant where the cold is most 

 severe : that both as regards the number of species and mass- 

 occurrence, lichens are " very far from covering all the soil on moun 

 tain heights which is bare of all other competitors." He found that 

 the same conditions prevailed in rock-lichens, there being fewer on 

 the very high mountains than on the lesser altitudes. The paper 

 abounds in original observation, and shows how much of interest is 

 still to be learned about lichens and their habitats. 



The special thanks of British students are due to the author for 

 giving us his study in English. The reference (p. iii) to " Crombie, 

 British Lichens, 1894-1911 " requires correction. A. L. S. 



Ernst Oestrup's posthumous paper on the Freshwater Diatoms 

 from Iceland is based upon 572 samples of diatom-material, gathered 

 by some sixteen collectors mostly in the east, south, and south- 

 western parts of Iceland. The work is divided into two parts : (1) a 

 systematic list with references to literature and giving descriptions of 

 57 new species and 13 new varieties wliich are all figured in the 

 5 plates; and (2) an alphabetical list with tables showing the distri- 

 bution of all the 468 species and varieties in Iceland itself, and their 

 wider distribution in the Arctic region and in the five continents 

 of the world. The number of forms previoush^ recorded for the 

 island was 131 ; so its diatom-flora is now three-and-a-half times as 

 large. In an appendix is a list of the forms collected in hot springs ; 

 these include 178 species and varieties, representing 31 genera, and 

 for the most part they were found in the living state — that is, con- 

 taining endochrome. A. Gr. 



Water Plants^ a Study of Aquatic Auf/iosj^erms. By Agnes 

 Arbee, D.Sc, F.L.S. 436 pp. and 172 figures. Cambridge 

 University Press, 1920. 31s. Gd. net. 



It is always interesting to see how Modei'n Botan}^ of the Schools 

 will approach the subject of the indigenous flora, and explain what 



