POLLINATION AND FERTILIZATION 119 
Three of the nuclei at the other end also form three 
cells, the antipodal cells. The fourth nucleus from 
each end passes to the centre of the embryo-sac. There 
they fuse and form one nucleus—the SzconpARY Nv- 
cLEUS. The ovule is now ready for 
fertilization. 
81. Forms of Ovule.—There are 
several forms of ovule. 
(1) The orthotropous ovule (fig. 68) 
is straight, having the micropyle op- 
posite to the funicle. 
(2) The anatropous ovule (fig. 69) 
is inverted so that the chalaza is at 
the opposite end to the funicle, and 
the hilum next the funicle. 
(3) The campylotropous ovule (fig. 
70) is curved. 
82. Structure of the Pollen Grain. 
—A young pollen grain is unicellular, y,. 0 79 iis 
and the cell wall consists of twomem- = Grains Germina- 
branes or coats. The outer coat, the hheee 
EXINE, is cuticularized, and frequently Are a aan 
ornamented with various patterns. Darwin's ‘ Ble- 
: ments of Bot- 
The inner coat is the Intinz. After any”’.) 
a time, the nucleus divides into two, thus forming two 
cells. The smaller is the GENERATIVE cell, the larger 
the VEGETATIVE cell. There are no cell walls between 
these cells, but the generative cell lies freely in the 
protoplasm of the vegetative cell. 
When the pollen grain reaches the stigma, germina- 
tion takes place. The generative cell divides into two 
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