August, 1912 



KNOWLEDGE. 



(in damp places) cross-leaved heath {Erica tctralix^ — these 

 four Ericaceous species are the most abundant, but many 

 characteristic plants are associati'd with them. In constantly 

 wet places — for instance, where owing to local hollows the 

 groundwater reaches the surface and a bog is formed — peat 

 may accumulate to a greater depth than on the dry heaths, 

 and owing to its acid character there occur many species of 

 the moorland formation, though in very different proportions. 

 In this book, however, the various formations are not 

 treated merely as isolated elements in the vegetation ; the 

 relations of the different formations to each other are 

 indicated, and the processes by which one formation passes 

 over into another are fully illustrated, with references to 

 localities where such changes may be clearly traced. Heath- 

 land has in some cases arisen dc noi'O on the poorer sands, as 

 can be seen in various areas where lichens and mosses form a 

 layer of peat and act as pioneers for the typical hcathland 

 vegetation. In many cases, however, it is certain that the 

 heath formation has arisen as the result of the degeneration 

 of woodland ; this process may either have taken place in 

 prehistoric times, or may be actually going on at the present 

 day. The heath formation is in many districts constantly and 

 successfully invading and eventually replacing the natural 

 woodland of sandy soils. The main cause appears to be 

 the gradual impoverishment of the soil by washing-out when 

 the rainfall is twenty-eight Inches or more ; the typical plants 

 of the wood-" floor " are starved and give way before the 

 invasion of heath-plants ; the roots of these invaders mat 

 together the surface soil layers and prevent the access of 

 oxygen, and this leads to the accumulation of " acid humus " 

 or " dry peat " In place of the original mild humus of the 

 woodland soil. Thus we have the formation of a type of wood 

 with a heathy vegetation, poor in species, on a soil composed 

 of sand and dry acid humus or peat; and finally the roots of 

 trees are either prevented from obtaining sufficient food owing 

 to the continued washing-out of the soil, or are prevented 

 from growing deeply enough owing to the formation of a hard 

 layer of sand ("moor-pan") bound together by humous 

 compounds, and the trees themselves die out, so that the 

 woodland Is replaced by heath. On the other hand, in some 

 areas the heaths are being colonised by self-sown pine- 

 seedlings, so that here we have a process of natural 

 afforestation of treeless heathland. 



Fine areas of heathland, where these processes, as well as 

 the actual heath vegetation, may be well studied, occur In 

 various parts of the country, and — as in the case of the other 

 formations described In the book — readers will find detailed 

 references to localities for such studies in whatever part of 

 the British Isles they may be residents or visitors. For 

 instance, around London and within easy reach on the 

 " Surrey side " we find fine heath formations, with Illustrations 

 of the degeneration of woodland, encroachment of heath 

 vegetation, the oak-birch heath association, sub-spontaneous 

 pine-woods, and so on ; special mention may be made of the 

 heaths developed on the Lower Greensand, Bagshot sand, 

 and the overlying plateau gravels, at various points between 

 Dorking and Leith Hill on the east and Oxshott and 

 Weybrldge on the west. 



However, it Is unnecessary to Indicate further the nature of 

 the contents of this book, which should be obtained by every- 

 one Interested in plant-hfe. The names of the editor and his 

 collaborators are sufficient guarantee for the (juallty of this 

 " account of British vegetation from a standpoint which has 

 not hitherto been adopted in any general treatment of the 

 plant-life of this country," for they are one and all botanists 

 who have laid the foundations of Plant Ecology in this country, 

 and the most important results of their labours In this field 

 are Incorporated In the book before us. 



In addition to a list of recent papers on British vegetation, 

 the book is pro\ided with a full index of plant names and also 

 an admirable general Index. The low price of the book should 

 help In securing for It a wijde sale. The publishers are to be 

 congratulated on their enterprise In producing so reasonably 

 such a well got-up and splendidly-illustrated work, which 

 would not have been dear at a considerably higher price. 



F. C. 



StiuUcs ill Seeds and Fruits. — By H. B. Guppy, M.B- 



528 p.ages. 9-in. X 6-ln. 



(Williams & Norgate. Price 15/- net.) 



Thi; author of this book presents an enormous amount of 

 information relating to the absorption and loss of water by 

 seeds and fruits. In fact, one's first Impression Is that the 

 book is somewhat overloaded with columns of figures and 

 names of plants used in the author's simple weighing experi- 

 ments, and one cannot help thinking that much better, if less 

 copious, results would have been obtained had the author 

 used a small number of plants and a microscoije and a few 

 other methods of research, in addition to " the balance and 

 the oven, aided by a sharp knife and a pocket lens." There 

 is no doubt, however, that the author has made a most exten- 

 sive contribution of facts to a subject which has been but 

 little investigated, and has also suggested various lines along 

 which further research is desirable. Moreover, packed 

 though this book is with facts and figures, it is extremely 

 interesting and readable on account of the author's inter- 

 pretation of the facts and the speculations which he bases 

 upon them, and the reader who wishes to " skip " some of 

 the heavier parts of the book will welcome the author's con- 

 siderateness in providing a concise summary at the end of 

 each chapter. 



Probably many readers will regard the twentieth and last 

 chapter as the most Interesting in the whole book, dealing as 

 it does with " the cosmic adaptation of the seed." The 

 main theme of this chapter is that the seed offers a clue 

 to the conditions of life In other worlds, as contrasted 

 with the full-grown plant which Is adapted for terrestrial 

 life only ; the former points in the direction of the mini- 

 mum of life's possibilities, the latter toward the freest 

 conditions for growth. We have said that this book is 

 packed with details, but the details are all too nmch of one 

 kind ; they practically all deal with simple observations on the 

 changes in water-content of seeds and fruits during ripening. 

 The aspects of the subject to which the author has devoted 

 his attention are those most easily observed, and while inter- 

 esting in their way, they certainly do not throw much light on 

 the topics which the author attempts to handle In his specula- 

 tions regarding the " cosmical " features of seeds. It is 

 notoriously unsafe to build up elaborate theories on a too 

 limited basis of fact, and the author of this work has 

 evidently lost sight altogether of the chemical side of the 

 subject. The condition of the dormant dry seed is to a 

 large extent a matter for chemical Investigation. There are 

 only two alternatives with regard to the latent vitality of seeds — 

 either vital processes (Involving chemical changes) are still going 

 on continually through slowly, or else all change is at a stand- 

 still. Which of these alternatives Is correct has not yet been 

 determined, and apparently can only be determined by keep- 

 in? dry seeds in a vacuum and testing them at intervals during 

 a long period, as it is proposed to do with the seeds deposited 

 by Becquerel at the Bureau of Standards in Paris. Mean- 

 while, however, various chemical and physiological facts make 

 it extremely improbable that even the protoplasm of any dry 

 resting seeds can retain its vitality for much longer than did 

 the veteran seeds tested by Becquerel, and found to germinate 

 after eighty-seven years of repose in a herbarium. In the 

 respiration of certain plants, no oxygen is taken from outside, 

 while in the case of succulent plants respiration occurs with- 

 out any carbon dioxide being given out, and — as suggested by 

 Dr. F. F. Blackman (New Pliytologist, vol. 8, p. 35) — it is 

 quite possible that in the latent protoplasm, a steady though 

 small supply of energy might be set free, without any change 

 being caused In the surrounding medium. Such a process 

 would of course end, after a number — probably a com- 

 paratively short number — of years. In death of the protoplasm. 

 Again, it has of course been proved that dry dormant seeds, 

 spores of Bacteria, and so on, can endure extreme cold, but It 

 does not follow that no chemical changes can take place in 

 the protoplasm of cells exposed to the lowest temperatures. 



The seed is an organ of the greatest interest from many 

 points of view — morphological, physiological, phylogenetic, 



