156 BOTANICAL GAZETTE [SEPTEMBER 
However, such a discussion does not lie within the scope of this 
paper. 
That gymnosperms have been derived from pteridophyte 
_ stock is hardly open to discussion, at least we must assume that 
this is true, or all attempts at phylogeny are useless. The first. 
question which confronts us, therefore, is whether the very 
divergent gymnosperm lines have had a common origin in this 
pteridophyte stock or not. Was there a single group of archaic 
gymnosperms, derived from pteridophytes, which subsequently 
differentiated into distinct lines? The existing gymnosperm 
groups are so very diverse that one of two things seems evident: 
either they differentiated into divergent lines from a common 
gymnosperm stock in very ancient times, or they originated 
independently from the pteridophyte stock. From this discus- 
sion I wish to exclude the Gnetales, as we do not possess suffi- 
cient data concerning their early history, or concerning the 
morphology of the very dissimilar living forms, to justify any 
opinion as to their origin. They are such dissimilar fragments, 
living in such extreme conditions, that their origin is totally 
obscure. In some respects they are more cycad-like than coni- 
fer-like, but in most respects they are so unlike both that a sep- 
arate origin seems possible. It may be even true that the three 
genera belong to groups of independent origin, which is cer- 
tainly the easiest way of disposing of their differences ; and 
their common characters of true vessels, the so-called perianth, 
and elongated micropyle, may have been attained independently 
as readily as was heterospory ; but the combination of characters 
in common does not seem to justify such a disposition of them, 
and the three genera had better be regarded as of common 
derivation, wonderfully diversified by ancient separation, isola- 
tion, and extreme conditions. 
Approaching the subject from the historical standpoint, the 
great group Cordaites seems to be the first with sufficient data 
to justify consideration. The structure of the vascular bundles, 
especially those of the leaves, is said to suggest those of coni- 
fers, cycads, Isoetes, and Ophioglossum; and the sporophylls 
