460 PHARMACEUTICAL BOTANY 
through the elongation of its tube cell to form a pollen tube which 
grows into the nucellus (megasporangium). ‘Then, the genera- 
tive cell divides into a stalk cell and a body cell. The body cell 
then divides to form 2 top-shaped antherozoids, each of which 
bears many cilia along a spiral grove. The mature pollen tube and 
its contents represents the male gametophyte of Zamia. 
. 
bas sbi eee a Dae ee 
4 D 
Fic. 347.—A, mature carpellate strobilus (cone) of Zamia. B, megasporophyll 
bearing two megasporangia. C, lengthwise section of a young megasporophyll, 
showing an early stage in the development of female sexual plants or megagameto- 
phytes. D, similar section of a later stage; megagametophytes fully matured. 
(From “A Textbook of General Botany” by Smith, Overton @ Co. by permission from 
Macmillan Co., publishers.) 
The female gametophyte develops within the megaspore (embryo 
sac) of the nucellus of the ovule by a series of nuclear divisions 
of the remaining nucleus within the embryo sac, resulting in 
many scattered nuclei within the cytoplasm. Cell walls are laid 
down and many cells result, and the embryo sac increases in 
size forming a prothallus. The nucellus is encroached upon by 
the enlarged developing gametophyte or prothallus in whose cells 
nourishment is stored. An archegonial chamber appears between 
the end region of the prothallus and nucellus, in line with the 
