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¬ 
normalities, 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 abnormal developments which may be shown 
in the various tissues of organisms. 
One could certainly reconstruct a remarkably fantastic ances¬ 
tral group of angiosperms or gymnosperms, were one to give 
weight to the multitude of monstrosities continually appearing 
in both vegetative and reproductive parts. 
