

SPERMATOPHYTA 417. 
young, like those of ferns. In certain species fernlike vascular 
bundles are found in the leaves. Even the megasporophyll of 
Cycas revoluta bears some resemblance to the frond of a fern. 
In former geologic ages the cycads were much more numer- 
ous and important than at present, but they have been crowded 
out by the development of higher types, and today we see only 
a remnant of what was 
once an important group. 
ORDER GINKGOALES 
This order is repre- 
sented by a single living 
species of Ginkgo, native 
of China and Japan, but 
now widely cultivated in 
temperate countries. 
Ginkgo is of interest 
as showing characters in- 
termediate between those 
of the cycads and the con- 
ifers. It resembles the conifers in general habit, as it is a tall, 
branching tree. The stem, like that of the conifers, has a small 
pith and a wide, woody cylinder. In the size of its fan-shaped 
leaves Ginkgo also approaches the conifers. The megasporan- 
gium is very much like that of the cycads (Figs. 470-472), and 
fertilization is by means of motile spermatozoids formed in pollen 
tubes. Among living seed plants motile spermatozoids are found 
only in the two most primitive existing orders of gymnosperms, 
the Cycadales and Ginkgoales. When Ginkgo is compared with 
the cycads and the conifers, it is found to be closer to the latter 
in general vegetative structure and to resemble the former in the 
character of the megasporangium and the method of fertilization. 
Relationship. Ginkgo, while having characters which make it 
intermediate between the cycads and the conifers, does not 
appear to have been derived from cycads or to be ancestral to 

Fic. 470. Ginkgo biloba 
End of branch bearing young leaves and young 
megasporangia. (X 4) 
