SEED-BEARING PLANTS 4OI 
studied, but possess only two neck cells, and no neck-canal 
cells. The large egg-cell in the venter is the largest known 
in the plant kingdom. 
FIG. 298. Cycas circinalis. Diagram of longitudinal section of a 
nearly mature seed; o, outer fleshy layer, with a bundle (0 1 ) of the outer 
vascular system; s, stony layer of integument; i, inner fleshy layer, with 
a bundle (i 1 ) of the inner vascular system; c, central vascular bundle. 
(After Marie C. 'Slopes.) 
357. Male Gametophyte. The germination of the 
microspore and the development of the male gametophyte 
involve only cell-divisions, but not the growth of new 
tissue. The mature gametophyte is called a pollen- grain. 
It consists of three cells: a prothallial cell, a tube-cell, 
and a generative cell (Fig. 299). There is no structure 
that can be positively identified as an antheridium, unless 
the prothallial cell is considered (as by some), as repre- 
senting the antheridium. The pollen-grain has two 
coats an outer and an inner. 
358. Pollination. When the pollen is mature it is 
scattered by the wind, and some of the grains lodge, by 
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