Knowledge. 



With which is incorporated Hardwicke's Science Gossip, and the Illustrated Scientific News. 



A Monthly Record of Science. 



Conducted by Wilfred Mark Webb, F.L.S., and E. S. Grew, M.A. 



JUNE, 1913. 



PROBLEMS OF PLANT LIFE. 



1. EVOLUTION AMONG LOWLY FORMS (THE ALGAE). 



By S. REGINALD PRICE, B.A. (Cantab.). 



Ever since the publication of Darwin's great work, 

 one of the chief aims of the biologist, in studying 

 organic nature, has been the establishment of a 

 scheme indicating the real evolutionary relationships 

 of forms, or, to use the more stereotyped expression, 

 a natural system of classification. 



In the plant kingdom certain lines and tendencies 

 within the great groups have been established with a 

 high degree of probability, chiefly from evidence of 

 comparative development, of reproductive structure, 

 and of the fossil record. Of the origin of the great 

 groups themselves, theories and speculations have 

 been numerous ; but they are nothing more than 

 bare possibilities, and, perhaps, hardly that in some 

 cases. If, as seems rather probable, all plants 

 evolved from a common stock, the divergence took 

 place countless ages ago, but the voice of the rocks 

 is silent on this question. 



Assuming, however, such a common group, it is 

 almost certain that its members were aquatic, and so 

 it seems reasonable to expect that the more primitive 

 members of our existing flora will be found in such 

 an environment. All the evidence goes to show that 

 the Algae as a group — comprising plants almost as 

 simple as may be imagined as well as the quite 

 complex bodies of the higher seaweeds — have never 

 lost their aquatic habit, and so, presumably, the 

 group as a whole has not suffered that great change 

 in the course of evolution which must have accom- 



panied the adoption of the terrestrial mode of life. 

 It has, therefore, been interesting to examine this 

 group carefully, with a view to throwing some light 

 on the evolution of plant-forms within it, and thus 

 indirectly obtaining a dim and indistinct reflection 

 of the process of elaboration of the "Proto-plants." 



The evidence has been confined to the study of 

 existing species alone, for the few fossil Algae, often 

 of very doubtful identity, are quite useless as indica- 

 tions of the phylogeny of the group. When, there- 

 fore, an evolutionary line is spoken of in this 

 connection, it must be remembered that it represents 

 a series of related species, not necessarily and most 

 often probably not directly related in a single line of 

 descent, but nevertheless giving an indication of the 

 tendency which has led to the elaboration of the 

 various forms. Exactly what is meant may be 

 illustrated by considering several obviously related 

 forms, which may be indicated by the letters 

 A to G, the last being presumed to possess the 

 most complex organisation of the series. Without 

 considering the factors at work, there is reason to 

 suppose that the form A has retained more primitive 

 features and undergone less alteration than B, and 

 so for each succeeding form, the climax of the series 

 being represented by G. The diagram (Figure 208) 

 represents this in a crude manner ; the lines running 

 from left to right indicate progressive evolutionary 

 tendencies, while those running vertically indicate 



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