i;6 SCIENCE PROGRESS 



the growth of plants. The second edition differs from its predecessor mainly in 

 the inclusion of this chapter, but various smaller sections have been interpolated 

 dealing with recent developments of other parts of the subject. 



Dr. Russell's book occupies a unique position in the literature of agriculture, 

 while it has also become indispensable to workers on the ecology of plants, as well 

 as to plant physiologists. It is impossible in the space available to analyse the 

 contents of this invaluable monograph, which is, moreover, already too well known 

 to those interested in soil investigation to require further commendation. The 

 new chapter gives a detailed and lucid account of the knowledge already gained, 

 besides indicating the gaps which remain to be filled by co-operative investigations 

 from various sides, regarding the remarkable inter-relationships between the 

 various classes of soil micro-organisms on one hand and the relations between the 

 entire micro-organic soil population and the growth of plants. Recent work has 

 opened up an attractive and important field of reseach and has indicated not 

 merely the unexpectedly large number and variety of the constituents of the soil 

 flora and fauna and their remarkably wide distribution in the soil of all parts of 

 the world — the latter fact, not commented on by the author, has been proved 

 particularly in the case of soil fungi as well as soil bacteria, and may well be 

 found true of the soil flagellates, protozoa, etc. — but the extreme complexity of 

 their relations to each other and to plant growth. These relations have been 

 as yet only in small part worked out, partly owing to the difficulty in isolating 

 the organisms and the greater difficulty in determining their actual behaviour 

 in the soil itself and in applying the results obtained by their isolation and 

 culture to the unravelling of the problems presented by the soil population. 

 The author makes a provisional segregation of the organisms into three 

 groups — those affecting plant growth directly or indirectly, those not acting 

 on plants but on the organisms of the first group, and those (none yet known with 

 certainty) which act neither on the plant nor on the first and second groups. 

 The nature and behaviour of each group are discussed, and details are given of the 

 remarkable results obtained by partial soil sterilisation. 



It might be suggested that in the case of monographs like those of the series to 

 which this book belongs a practicable plan would be to publish at fairly frequent 

 intervals inexpensive unbound supplements giving additions and corrections 

 resulting from current investigation of the subject, either instead of or (in fairness 

 to possessors of the first issue of the book) in addition to a new edition. Such 

 supplements would be in harmony with, and further considerably, the object aimed 

 at by the editors of these invaluable monographs, and would afford a satisfactory 

 solution of the question that must present itself in the case of branches undergoing 

 rapid development — whether to allow the book to get out of date or to issue new 

 editions at relatively short intervals. 



F. Cavers. 



All About Leaves. By the late Francis George Heath. [Pp. ix + 226, 

 with 4 coloured plates and 89 other illustrations.] (London : Williams & 

 Norgate, 1914. Price 4s. 6d. net.) 



Like the rest of the late author's numerous books, this posthumously published 

 volume indicates at any rate his ardent love of nature, his ingenuous and reverent 

 frame of mind, and the tinge of mysticism which caused him to dwell at every turn 

 on the mystery of things. The letterpress can hardly be made the subject of 

 criticism, however, and we need only add that the book is attractively illustrated, 



