PROBLEMS OF PLANT MORPHOLOGY 91 



from leaves in structure and function as to deserve a separate mor- 

 phological category, the same claim cannot be made for stamens 

 and carpels. They are very ancient structures of uncertain origin, 

 for it is quite as likely that leaves are transformed sporophylls as 

 that sporophylls are transformed leaves. ... To call a stamen a 

 modified leaf is no more sound morphology than to call a sporangium 

 derived from a single superficial cell a modified trichome. The cases 

 of ' reversion ' cited are easily regarded as cases of replacement. Lat- 

 eral members frequently replace one another, but this does not mean 

 that one is a transformation of the other." 1 



We see that in this verdict the emphasis is laid on the historical 

 development, but at the same time this is pointed out to be unknown 

 to us. With this latter conclusion I am in complete harmony, but 

 the accentuation of the historical-phylogenetic factor has, on the 

 other hand, led to a conception of the ontogenetic problem, in which 

 I can perceive no advance upon the old morphology; there is rather 

 avoidance of the problem than an attempt to solve it. This, however, 

 is connected with the purely formal conception, as the phylogenetic 

 morphology employs it. Let us examine the matter in question. 

 For a long time we have known that often in the room of the sta- 

 mens to confine ourselves to these flower leaves, or foliage 

 leaves, or occasionally even carpels, arise. The idealistic morphology 

 says that this proves that the stamens are "leaves," for these can 

 be modified the one into the other. Coulter and Chamberlain, how- 

 ever, deny that a stamen fundament may be transformed into a 

 flower leaf; they find only a "replacement" of one "lateral member" 

 by another. It should be remarked that "leaves" exist in nature 

 as little as "lateral members." Both notions are mere mental ab- 

 stractions, not the expression of the facts of observation. We speak 

 of the replacement of one organ by another if these have nothing 

 more in common than the place of origin. Thus we see that in the 

 foliose liverworts a branch often arises in the position of a leaf-lobe. 2 

 No one has observed any intermediate form between these; the 

 lateral shoot in reality takes only the position of a leaf-lobe. The 

 relation between the stamens and the organs which "replace" 

 them is, however, quite different. We speak of a transformation 

 of an organ A into an organ B when B not only stands in the position 

 of A , but also corresponds with A in the earlier stages of its develop- 

 ment, and later strikes out on its own line of development. If this is 

 the case, we should expect to find between A and B intermediate 

 forms which are different according to the developmental stage at 

 which A is caused to develop further as B. To use an analogy: 



1 Coulter and Chamberlain, Morphology of the Angiosperms, p. 22. 



2 Goebel, Rudimentare Lebermoose, Flora, 1893, p. 84. Ueber die einfachste 

 Form der Moose, ibid. 76, 1892, p. 92. 



