April, 1913.] The Classification of Plants, IX. 103 



stalk with its numerous anthers being a compound microsporophyll 

 homologous to those of the Bennitales and the cycads. On the 

 other hand, the sporebearing structures of the Gneteae are regarded 

 as highly specialized strobili, the whole cluster being an inflores- 

 cence. If these views are correct, we have in a general way the 

 same evolutionary developments in . the gymnosperms as are so 

 evident in the angiosperms. There are, however, no great number 

 of transition types as we have in the angiosperms, where one can 

 follow through from the primitive strobilus-like flower to a 

 highly reduced and specialized inflorescence, with numerous 

 vestiges, pointing out the probable course of evolution. 



The arguments usually advanced from the presence of ab- 

 normahties, as stated above, are far from convincing. The 

 change of one organ to another, or the appearance of a structure 

 peculiar to one organ on another, simply mean that the hereditary 

 factors have become active in a tissue where they are normally 

 inactive or latent. One would certainly not claim that when 

 the stamen of a rose or other flower is transformed into a petal 

 there is a revision to a primitive condition. For this would give 

 us a primitive flower composed entirely of petals. It is evident 

 however, that the evolution of the rose and all other similar 

 flowers must have proceeded in the opposite direction. Instead 

 of a reversion we have in such cases only the expression of resi- 

 dent factors in structures where we do not expect them to be 

 operative. The petal factors are present, potentially, in every 

 cell of the entire plant body. 



Because a petiole under an abnormal stimulus, caused by 

 certain bacteria or by special manipulation, may develop stem 

 structures is no evidence that the petiole was phylogentically 

 ever a stem. If one finds stem-like tissues in the carpel petiole 

 of Ginkgo, there is no unquestionable evidence that the organ was 

 phylogenetically a stem. The stem structure may have developed 

 as a response to the parasitism of the gametophyte and its embryo. 

 It is also true that in the great majority of supposed phylogenetic 

 reversions, there are after all no hereditary characters shown in the 

 abnormal structure but what appear in the normal ontogeny. 

 Usually there is simply an abnormal distribution in the expression 

 of such characters. If a root under an unusual manipulation 

 can give rise to tissues which produce flowers, this does not mean 

 that in its past phylogeny the root was a petaliferous organ. 

 Yet such interpretations are continually made by some biologists 

 to account for any abnomial developments which may be shown 

 in the various tissues of organisms. 



One could certainly reconstruct a remarkably fantastic ances- 

 tral group of angiospemis or gymnospemis, were one to give 

 weight to the multitude of monstrosities continually appearing 

 in both vegetative and reproductive parts. 



