212 
THE LIFE OF FLOWERING PLANTS 
tion. For this reason farmers and gardeners should know 
the habits of the insects which pollinate flowers and the best 
way to plant certain crops to secure the results desired. 
193. How Fertilization Is Accomplished. — When pollen 
grains fall on a stigma they are held there by a sticky sub¬ 
stance or by projections, 
and each soon puts forth 
a tube as already ex¬ 
plained. The tube makes 
its way through the style 
either by means of a 
channel which traverses 
it or by making a path for 
itself through the loose 
tissue of which styles 
without channels are 
composed. The nuclei 
are always near the end 
of the tube, which may 
become very long com¬ 
pared to the size of the 
grain which produced it. 
(See Figure 195.) When 
it reaches the ovary it 
A , pollen tube ; B, micropyle ; C, outer turns towards an ovule 
integument ; D, inner integument ; E, em- which it enters usually 
C ’ fSmale throu S h the micropylar 
opening. When the tip 
of the tube containing the male nucleus touches the egg 
cell in the embryo sac, it bursts, and its nucleus unites 
with that of the egg cell, completing the act of fertilization. 
The ovule at the time of fertilization consists of a mass of 
tissue known as nucellus (Latin, nucella, small nut), which is 
enclosed by an outer and an inner integument (Latin, in, 
upon, tego, cover) except at one point, the micropylar open- 
Ovule in Act of Fertilization. 
