THE MORPHOLOGICAL COMPOSITION OF PLANTS. 81 



Phanerogams, whether it may not rather be regarded as a 

 parallel development along another line of descent from the 

 Green Alga?. 



" Hence we must look for the origin of the shoot-structure 

 of flowering plants in the sporophytes of the Pteridophytes, 

 from which group there is no reason to doubt that the 

 phanerogams have arisen in descent. The various groups of 

 Pteridophytes vary much in the organization of these shoot- 

 systems, as a mental glance at the types exhibited by the 

 Ferns, Horse-tails, Club-mosses, Ophioglossacece, and the iso- 

 lated Isoetes will convince you at once. It may be that 

 some of these groups are independent in descent, i.e., that the 

 Pteridophyta are polyphyletic, and the current hypothesis 

 with regard to the phanerogams is that they have arisen by 

 two, if not three, separate lines of descent from different 

 groups of Pteridophytes (this is indicated in the classificatory 

 diagram on p. 377 of vol. I). I should not, however, care to 

 pin my faith to these or to any such lines of ancestry. Still 

 I think we must look for the ancestors of the Flowering 

 Plants among the Pteridophytes, and the latter always 

 have a good distinction between axis and appendages. The 

 problem of the evolution of these differentiated sporophytic 

 shoots is undoubtedly the - great outstanding problem of 

 morphology. Various attempts have been made to solve it, 

 of which probably the most important is the theory of Profs. 

 Bown and Campbell, who derive the Pteridophytes from some 

 Liverwort like Anthoceros, but the sporophyte of course 

 from the sporophytic portion of the plant (not much more 

 than a spore-capsule), the prothallus of the Fern representing 

 the vegetative thallus of Anthoceros. I am not wholly con- 

 vinced by these undoubtedly ingenious hypotheses, in support 

 of which an immense amount of facts have been collected; 

 but my position would, I know, simply ' put us to ignorance 

 again ' on this question. 



" I have discussed this at some length in order to bring 

 out clearly the immense difficulty of constructing a well- 

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