162 EVOLUTION OF PLANTS 
THE GYMNOSPERMZ 
In the Gymnosperms the flowers are of the simplest 
character, consisting entirely of sporophylls of one 
kind. Macrospores and microspores are always borne 
in different flowers and very often upon different plants. 
THE Cycaps (Cycadacee) 
Without question the lowest types of seed-bearing 
plants known are the Cycadacezx, a group of palm-like 
plants of which the best known is the so-called “sago- 
palm” of the greenhouses, Cycas revoluta. About sev- 
enty-five living species of Cycads are known, widely dis- 
tributed through the warmer regions of both the Old and 
the New worlds. Most of them are strictly tropical, but 
one species, Zamia integrifolia, is found as far north as 
Florida, and Cyeas revoluta probably extends beyond the 
northern tropic in Japan. They recall in many ways 
certain ferns, and a careful examination of the tissues 
of the sporophyte shows that these resemblances are 
more than superficial. The tissues of the fern-like 
leaves resemble those of the lower ferns, and the leaves 
when young are coiled up much as in the ordinary ferns 
(Fig. 40, F). The plant, however, may develop a 
primary tap-root like that of the Conifers or Dicotyle- 
dons, and there is a more or less marked secondary 
thickening of the vascular bundles of the stem, which, 
however, also occurs in a few ferns. 
In Cycas the macrosporangia are borne upon leaves 
which differ but slightly from the ordinary ones (Fig. 
40, A). The sporangia are very large, sometimes being 
