1898] THE ORIGIN OF GYMNOSPERMS 161 
fact that Ginkgo is no longer regarded as a conifer, Long 
before the evidence of spermatozoids was discovered it seemed 
perfectly clear to me that Ginkgo was more cycad-like than 
conifer-like. In the light of our present knowledge the appear- 
ance of Ginkgo in association with the Carboniferous cycads 
seems natural enough. It is a matter of very secondary impor- 
tance whether we are to regard it as an independent line or not. 
I am inclined to believe that while during the Paleozoic hetero- 
spory and the seed were both attained, siphonogamy was in 
its beginnings, and that the spermatozoid habit was for the 
most part still continued in the seed lines. There is no conclu- 
Sive evidence, therefore, that any of our modern coniferous 
genera appeared during the Paleozoic, during which the Cor- 
daites were the dominating seed plants. During the last Palzo- 
zoic periods undoubted conifers did appear, and in considerable 
abundance, and we may recognize the beginnings of distinct 
lines represented today by Abies and its allies, Taxodium and 
its allies, and Taxus and its allies, but the genera are not those 
of today. In the lower Mesozoic, however, modern araucarian 
and abietinous genera appear; and the Taxodium and Taxus 
lines become more distinct, but not modern until the later Meso- 
zoic. At that time Cupressus forms also appear, but not of 
modern genera. Further details are not necessary, as the point to 
be made is that the conifer type was not recognizable until late in 
the Paleozoic, and then not in its modern expression. It cer- 
tainly suggests a later departure from the Cordaites stock than 
do the cycads. 
Another fact is interesting to note in connection with the 
evolution of the conifer forms. In existing conifers there is 
considerable variation in the development of the male gameto- 
phyte. In some forms, as the Abietinee, the development of 
two or three prothallial cells, distinct from the large antheridial 
cell, is a well-known fact, an amount of prothallial develop- 
ment not shown by any other living heterosporous forms, even 
the heterosporous pteridophytes. In other forms, as Cupres- 
sinee and Taxez, the reduction of the male gametophyte is 
