SEED PLANTS 175 
Cycads and Conifers, but on the whole they are prob- 
ably nearer the latter. 
SUMMARY 
Compared with the Angiosperms, the Gymnosperms 
are an ancient primitive group of plants showing very 
evident resemblances to the Pteridophytes, from which 
they have doubtless originated. It is not likely that the 
existing Gymnosperms constitute a homogeneous class, 
but it is more probable that they are remnants of at 
least three lines of development. Of these the Cycads 
show evident relationships to the ferns, this being 
evinced by the character of the leaf and flowers, and 
still more by the form of the spermatozoids. The geo- 
logical record shows that the Cycads were once a much 
more important group than at present. Perhaps related 
to these is the genus Gingko, also a very old type, with 
but a single living representative. 
The Conifers are a more recent type than the Cycads, 
but still are older than the Angiosperms. In the gen- 
eral habit of the sporophyte, especially the sporophylls, 
they suggest a direct connection with the Lycopods, 
and this is borne out by a study of the gametophyte, 
which closely resembles that of Selaginella. The pres- 
ence in the Carboniferous rocks of gigantic Lycopods 
now extinct, suggests these as possible ancestors for the 
existing Conifers. 
There is very little in common between the third 
order, the Gnetacez, and the other Gymnosperms, and 
it is questionable whether the theory that the Gnetacex 
