April, 1913.] 
The Classification of Plants, IX. 
105 
carpel also shows successive degrees of specialization. The cones 
and ovuliferous scales of the white pines show an intermediate 
type of development between those of the spruce and Douglas- 
fir on the one hand and the more specialized two-leaved pines on 
the other. 
By some, relationships and phylogenies are interpreted mainly 
through supposed similarities of the vascular structures. Such 
classifications are, however, vain unless they are supported by 
the combined evidence of all other structures, at least until it 
can be shown that the extremely hypothetical assumptions used 
as a basis for interpretation can be established with some degree 
of probability. There are no primitive vascular plants known, 
as indicated above, which might be used as a basis of comparison. 
The fossil record is a blank for any plants which would lead us to 
the beginning of vascular evolution and the lowest living 
Homosporous Pterdophytes show a considerable diversity. 
The living homosporous classes are about on a general level of 
evolutionary development and the assumption that the protostele 
or any other type of vascular structure is the most primitive 
remains to be proven. There is also no evidence that the vascular 
system or any other stem structure is less subject to modification 
than are leaf, root or reproductive structures, none of which have 
escaped changes of a profound nature. The assumptions based 
on the embryogeny of the vascular structures are no more certain 
than those based on the embryogeny of the reproductive parts. 
Nevertheless, the careful study of the vascular systems will give 
us another important aid in deciphering the true relationships 
of the higher plants, provided that the knowledge gained is cor¬ 
related with evidence from other lines of investigation. It is, no 
doubt, permissable to call supposed embryonic recapitulations 
to our aid in attempting to reconstruct the hazy course of phylo¬ 
genetic history, but it must be regarded as only one of the lines of 
evidence to be considered along with every other clue one may 
obtain from every structure, function, and peculiarity of the plant 
in its entire life cycle. 
Synopsis of the Cycadophyta. 
I. Leaves compound; stem an unbranched shaft or with few branches. 
1. Megasporophylls only slightly differentiated from the foliage 
leaves; leaves fernlike, often very much compounded; no cones 
formed. (Fossil). Pteridosperme:. 
2. Megasporophylls highly specialized, usually very different in 
form from the foliage leaves; in Cycas still showing some foliage 
characteristics; leaves pinnate, rarely bipinnate; at least one 
kind of sporophylls in cones. Cycade/E. 
a. Microsporophylls leaflike; flowers probably all bisporangiate. 
(Fossil). BENNETTITALES. 
b. Microsporophylls not leaflike, arranged in compact mono- 
sporangiate cones; diecious. CYC AD ALES. 
