SPERMATOPHYTES 
267 
MALE GAMETOPHYTE 
Development. In the development of the male gametophyte of 
angiosperms no vegetative cell appears (except in very rare cases), so 
that the gametophyte is reduced to an antheridium, and the pollen grain 
is an antheridium initial 
(fig. 595). The first 
division of the nucleus 
of the microspore pro- 
duces the generative and 
tube nuclei, and this is 
the usual condition of 
the pollen grain at shed- 
ding (fig. 596). The 
generative cell is usually 
organized as a naked 
cell, which assumes vari- 
ous forms, generally 
from spherical to lens- 
shaped. This cell may FlGg 59S _ 598 . _ Male gam etophyte of angiosperms, 
divide before the shed- as shown bySilphium: 595, pollen grain, with its single 
ding of the pollen grain nucleus and spiny outer coat; 596, first division, forming 
1.1 , generative and tube nuclei (shedding condition in many 
n , ^ 3 cases); 597, second (and last) division, resulting in the 
nuclei are observed two male cells from the generative cell (shedding con- 
within the mature grains c^ 011 i n some cases), a division which often occurs in the 
,,~ ^ ., j. ., pollen tube; 598, the two male cells having elongated. 
(% 597); or it divides ^ ter MER] ^/ 
after passing into the 
pollen tube. The generative cell is the primary spermatogenous cell, 
and there is only one division, resulting in two equal male cells. 
The gradual reduction in the number of spermatogenous cells pro- 
duced by the antheridium of a heterosporous plant has reached its ex- 
treme expression among angiosperms. In Selaginella the generative 
(primary spermatogenous) cell produces a large number of mother cells, 
each of which produces a sperm. In Isoetes the generative cell produces 
four mother cells, each of which develops a sperm. In cycads and 
Ginkgo the generative cell produces three cells (by two successive divi- 
sions), two of which are mother cells developing sperms. In conifers 
the generative cells produce the same number and character of cells as in 
cycads, but the two mother cells do not develop sperms, functioning 
