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SPERMATOPHYTA 423 
The three apical megaspores degenerate, while the basal 
one germinates (Fig. 452) and produces a female prothallus 
(Fig. 453) which, as in all of the spermatophytes, remains 
permanently inclosed 
within the megasporan- 
gium. The female pro- 
thallus is a white, oval 
mass, at the apical end 
of which archegonia are 
produced. A mature 
archegonium consists of 
a large egg cell and the 
neck cells (Fig. 480). 
At one stage there is 
an evanescent ventral- 
canal cell. A compari- 
son of the cycads and 
the pine shows that the 
general structure of the 
ovules and female pro- 
thalli is very similar in 
the two cases. 
Microsporangium. ‘The 
microsporophylls are 
small and borne in 
small cones (Fig. 481). 
Each has two microspo- 
rangia on its under sur- 
face. The male cones 

Fic. 478. Pinus insularis forming an open 
forest in the mountain region of Luzon, in the 
Philippine Islands 
occur in clusters near the ends of the long branches and, like the 
short branches, are produced in the axils of the scale leaves on. 
the long branches (Fig. 481). 
Pollination. The microspores (pollen grains) are carried by 
the wind and deposited in the micropyles of the megasporangia. 
This process is known as pollination. At the time of pollination 
the female cone stands erect and the scales are spread apart 
