4IO STRUCTURE AND LIFE HISTORIES 
in frequently not having the embryo develop until after 
the seed is planted, and in not having the embryo undergo 
a period of rest between its formation and its final develop- 
ment into a mature sporophyte ; the absence of an embryo 
characterizes some of the fossil relatives of Cycas. 
The genus Cycas is the only living genus of plants which 
produces seeds without developing either a cone or a flower, 
but produces the seeds on sporophylls borne on the main 
stem. It is the simplest of all living seed-plants, to this 
extent, being in this respect as lowly organized as 'the 
ferns. 
OUTLINE OF LIFE HISTORY OF A CYCAD 
The Cycad plant 
(Sporophyte) 
44 44T 
Microsporophylls Megasporophylls 
4< -4r * 4' 
Microsporangia Megasporangia (ovules) 
,4, < Reduction > J, 
Microspores Megaspores 
4 4 
Male gametophyte Female gametophyte 
(Pollen-grain) (Endosperm) 
4 i. 
Vestigial antheridium Archegonium 
r 
Generative cell 
4 
Sperms 
?oni 
I 
Oosperm 
44 
Embryo 
44 
New Cycad plant 
(Sporophyte) 
