166 EVOLUTION OF PLANTS 
they occur in great numbers. The oldest forms closely 
resembled the existing genus Cycas, which has persisted 
while many of the more specialized types have become 
quite extinct. 
Perhaps allied to the Cycads, and like them also 
a very old type, is the curious genus Gingko (Fig. 
41, H), represented at present by a single species no 
longer known ina wild state, but much planted about 
temples in China and Japan, where gigantic trees, hun-. 
dreds of years old, are standing. From the fern-like 
venation of the leaves, the tree is sometimes called the 
maiden-hair tree, and this peculiarity of the leaves prob- 
ably indicates a real affinity with the ferns. Many fossil 
species, much like the existing one, are known, the oldest 
ones from the Permian rocks, and therefore somewhat 
more recent than the oldest Cycads. 
Gingko is usually referred to the Conifer, but the 
development of the gametophyte, especially the produc- 
tion of multiciliate spermatozoids like those of Cycas, 
as well as the fern-like character of the leaves, suggest 
that its affinities are rather with the Cycads than with 
the Conifers. 
THE CONIFER 
Although the Cycads and Conifere are usually asso- 
ciated in a common group, Gymnosperme, it is at least 
doubtful in view of the recent discoveries in regard to 
the former, as well as because of other differences in 
structure, whether these two orders are really related to 
each other. 
The Conifere are the familiar “evergreen” trees of 
