“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, _Ophioglossaceæ_, and the isolated 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 convinced 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 wellgrounded theory of the origin of the differentiated shoot-system of the higher plant. I confess I don’t think it can be done at all with the materials at present at our disposal. Of course it is just possible to suppose that some ancestral sporophyte had the structure of a proliferous thalloid liverwort gametophyte, and that from it was evolved the phanerogamic shoot in the ways you suggest. This gives us absolutely no clue, however, to any Pteridophytic shoot, which ought to be intermediate (more or less) between the hypothetical ancestor and the Phanerogam, and is furthermore, as far as I can see, not supported by an atom of evidence of any kind. It is true that your theory fits in well with the phenomena exhibited by phanerogamic shoots themselves, but this fact you will see must lose much of its significance if the hypothesis lacks foundation.