86 PLANT MORPHOLOGY 



because the study of ontogeny only may proceed from the experi- 

 mental point of view. An understanding of development is possible 

 only when the conclusions to which the observation of the phe- 

 nomena of development has led us, rest upon experimental proof; 

 in other words, when we ask questions of nature, and obtain our 

 answers to them. 



Every little step and with such only are we now concerned - 

 beyond the mere descriptive consideration of development is here 

 of significance, and brings the possibility of further progress. And 

 small indeed, I may add, appears to be such advance to those who 

 from the beginnings of phylogenetic morphology have, like Sisy- 

 phus, sustained their courage to roll again and again up the moun- 

 tain the rock of phylogeny as often as it has rolled down. 



It may now be attempted to examine somewhat more closely 

 in certain particular examples the relation between phylogenetic 

 and causal morphology. One of the changes which phylogenetic 

 morphology has brought with it is that it seeks to ascertain which 

 form is "primitive" and which derived. 1 Idealistic morphology 

 has borne in upon us no conviction on this question, since it derives 

 all forms from a type which is present only as a conception. But 

 phylogenetic morphology must, on the one hand, always reckon 

 with the possibility of polyphyletic development, and, on the other 

 hand, it can operate not only with reversionary structures, as did the 

 idealistic morphology, but must be far more concerned in deter- 

 mining which forms within the series which it proposes stand near- 



1 I do not. of course, deny that there are forms which we may designate primi- 

 tive. What, however, is insisted upon in the above text is as follows: 



(1) The different meanings of the word "primitive." It can mean either 



(a) A form which stands nearer to the stem form than any other. In this 

 sense we may designate the Gymnospermcc, e. g., as more primitive 

 than the Angiospermce, because it may be admitted that all seed-plants 

 are derived from heterosporous Archegoniatce, while it is the Gymno- 

 spermcB which maintain this character most evidently. 



(fe) "Primitive" is also used often in the sense of "phylogenetically older." 

 At this point, however, we come into the field of hypothesis, for the 

 paleontological facts are far too few to afford us a picture of chronologi- 

 cal series of plant groups. It is known that there are several parallel 

 developmental series (e. g., the appearance of heterospory in different 

 groups of Pteridophyta) . Forms which appear primitive may, then, in 

 reality constitute the end of a very long series, younger perhaps than 

 one which does not appear to be primitive and is derived from other 

 stem-forms, with which then it is not genetically related. It is, e. g., very 

 easily conceivable, though at present incapable of proof, that hetero- 

 spory, in so far as it is older than isospory, arose at first from spores of 

 sexual cells (male and female swarm spores), and that from this point 

 on the development of the spores took on a more or less marked vegeta- 

 tive character. Were this the case, then the isosporous Pteridophyta 

 would be phylogenetically younger than the heterosporous, and the Bry- 

 ophyta would be a parallel development to the Pteridophi/ta. This is, ito 

 be sure, only a possibility which one may at first regard as fantastic, 

 which, however, is no more so than many other conceptions which have 

 been put forth at one time or another. 



(2) The difficulty of distinguishing with certainty between primitive and re- 



duced forms. 



