A WEEKLY ILLUSTRATED JOURNAL OF SCIENCE. 



" To the solid ground 

 Of Nature trusts the mind which builds for aye." — Wordsworth. 



THURSDAY, NOVEMBER 5, ic 



ALTERNATION OF GENERATIONS IN 

 PLANTS. 

 The Origin of a Land Flora. A Theory based upon 

 the Facts of Alternation. By Prof. F, O. Bower, 

 F.R.S. Pp. xii + 727; with numerous illustrations. 

 (London : Macmillan and Co., Ltd., 1908.) Price 

 lys. net. 



THIS important bool':, embodying the results of 

 the author's well-known morphological re- 

 searches during the last twenty years, may be 

 regarded from two points of view. On the one hand, 

 it forms a most excellent manual of comparative 

 morphology for the groups dealt with — essentially the 

 higher cryptogams ; on the other, it gives the final 

 statement of those theoretical views on the alterna- 

 tion of generations in plants with which Prof. 

 Bower's name is associated and of which he is the 

 leading champion. The two aspects cannot, however, 

 be kept separate; the theory forms the thread on 

 which the facts are strung, and without the theory 

 we should not have had those researches which have 

 so greatly enlarged our knowledge of the facts. In 

 this way the " working hypothesis " has fully justified 

 its existence, and all botanists owe a debt of grati- 

 tude to the author for the theory which he has so 

 systematically worked out, as well as for the detailed 

 investigations to which it has been the guide. No 

 more important contribution to scientific botany has 

 appeared in England since the revival of botanical re- 

 search in this country in the 'seventies of the past 

 century. 



It is needless to say that the author's presentation 

 of the facts is everywhere scrupulously fair; his book 

 may be used with profit and pleasure alike by those 

 who accept and those who dissent from his main posi- 

 tion. The reviewer cordially agrees with the con- 

 cluding sentence of the preface : — • 



" Whatever view be ultimately taken of the prime 



origin of the alternating generations, many of the 



conclusions arrived at here as to the morphological 



progress and phyletic grouping of the Archegoniatas 



NO. 2036, VOL. 79] 



will stand : they have a validity of their own quite 

 apart from any question of the ultimate origin of the 

 sporophyte, which has finally become the dominant 

 factor in the flora of the land." 



The book is divided into three parts: — Part i., 

 statement of the working hypothesis, 20 chapters, 

 254 pp. ; part ii., detailed statement of facts, 

 20 chapters, 402 pp. ; part iii., conclusion, 7 chapters, 

 60 pp. 



This arrangement involves a certain amount of 

 repetition, but, on the whole, is well adapted to the 

 purpose of the book, which is to state the main theory 

 with its subsidiary hypotheses, and to test them fully 

 in their application to the morphological data. 



In considering the book critically, attention will be 

 cliiefiy directed to its theoretical side. The reviewer is 

 one of those who are unable to accept the chief con- 

 clusions of the author, and hence it is impossible 

 altogether to avoid controversy. From what has 

 already been said, it will be clear that theoretical 

 differences in no way affect the high estimate of the 

 value of Prof. Bower's book which every unbiased 

 reader must form. 



After an introductory chapter on the scope and 

 limitations of comparative morphology, the life-history 

 of a fern is appropriately given the foremost place 

 as the type of the regular alternation of sexual and 

 asexual generations which characterises the higher 

 plants. In the ferns and the vascular plants gener- 

 ally the asexual generation is the plant itself, with 

 all its elaboration of vegetative organs, while the 

 sexual phase is represented by the comparatively small 

 and simple prothallus. In the Bryophyta (mosses 

 and liverworts), on the other hand, the balance of 

 the two generations is reversed, the main vegetative 

 development falling in the sexual stage, while the 

 asexual generation is merely a fruit (sporogonium) 

 dependent throughout life on the sexual plant which 

 bears it. In both classes " there is thus a marked 

 difference between these two phases, and their 

 sequence may be said to constitute an antithetic 

 alternation " (p. 32). Here, and in some other 

 passages (e.g. p. 658), the phrase " antithetic alter- 

 nation " is used simply to express the known facts 



