REVIEWS 489 



owing to war conditions, and this delay has made it possible to include more 

 recent interesting work on the subject-matter, e.g. it has allowed of the 

 inclusion of a discussion and criticism of Dr. Church's paper on The Symbiosis 

 of Lichens, a paper in which his views on the " subaerial transmigration " 

 are extended to this group in a manner from which our author dissents. 



The work begins with a comprehensive account of the history of lichen- 

 ology : Schwendener's theory of the composite nature of the lichen-plant is 

 here briefly mentioned. The more detailed consideration of this subject, of 

 the cultural work of Bonnier and Moller, and of the recent views of the rela- 

 tionship of the component parts of the lichen thallus expressed by Elenkin, 

 Danilov, and Paulson respectively, is left for the next chapter in which the 

 gonidia and hyphas are studied in detail. 



Then follows a very full account of the structure of the thallus and of the 

 structures — cephalodia, soredia, istdia, etc. — peculiar to lichens ; the various 

 methods of reproduction are next discussed. The vexed question of the 

 sexuality of the fungal component of the lichen is examined at some length ; 

 and comparisons are made with similar fungal forms. The author sums up 

 with Funfstiick's statement that fertilisation has not yet been proved, but 

 only rendered very probable. The recent observations, not here mentioned, 

 of Killian on Venturia, and of Dodge on a species of Ascobolus, go far towards 

 increasing this probability. Chapters on the systematics and phylogeny 

 of the group follow, the origin of the lichens and the relationship of the 

 different fungal partners being considered. 



A feature of the book which greatly impresses the present writer is the 

 manner in which each part of the subject receives its meed of attention. 

 This is exemplified in the space allotted by the author to the Physiology, Biono- 

 mics, Ecology, and Economics of this very interesting group. Economically, 

 except for their use as dyes, lichens are not very important at present ; but we 

 are presented with a very interesting account of their uses in past times. 

 Ecologically the group is an important one, lichens being prominent pioneer 

 forms, and this part of the subject is fully dealt with. 



The book is well illustrated, a number of reproductions of habital photo- 

 graphs being a welcome feature. A few of the figures appear to be a little too 

 diagrammatic; and the chapter on Systematics, strangely enough, is not 

 provided with any figures. A much-needed glossary, a bibliography, and an 

 index are provided. The volume treats comprehensively of an important and 

 interesting group, and makes an admirable addition to this series. 



E. M. C. 



Soil Conditions and Plant Growth. By E. J. Russell, D.Sc, F.R.S. 

 Fourth Edition. [Pp. xii + 406, with 5 plates and 28 figures in the 

 text.] (London: Longmans, Green & Co., 1921. Price i6s. net.) 



As this work has already been reviewed we need only note the changes made 

 since the last edition in 1917. That these are considerable may be gathered 

 from the fact that the 243 pages of that edition have now extended to 406, 

 though a great part of this difference is accounted for by reduction in the 

 size of the page. Perhaps the most important addition to this valued 

 classic is the provision of a more adequate index to the subject matter, and 

 also an index to the authors quoted. 



The changes in the general text are mainly those necessitated by the 

 advances in knowledge of the last few years, notably in the sections on 

 the micro-organic population of the soil, colloidal properties, soil acidity, etc. 



It is satisfactory to learn from the Preface that it is intended to maintain 

 the more general treatment here adopted, and that the detailed exposition 

 of special branches is to be dealt with in a series of monographs under the 

 editorship of Dr. Russell. 



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