246 A TEXT-BOOK OF BOTANY 
In this condition the stigma is said to be ready or mature. 
The pollen is mature when it is ready to fall out of the 
pollen sacs or to be removed from them. In obtaining 
nectar or pollen as food, the visiting insect receives pollen 
on some part of its body which will be likely to come in 
contact with the stigma of the next flower visited. 
Cross-pollinating flowers may be illustrated under three 
heads, distinguished from one another by their methods of 
hindering self-pollination; but it must be understood that 
almost every kind of flower has its own way of solving the 
problems of pollination. It is an exceedingly interesting 
and profitable exercise for the student to examine as many 
cross-pollinating flowers as possible, with the view of de- 
termining in each case how self-pollination is hindered, 
how, cross-pollination is secured, and how the visits of 
unsuitable insects are discouraged. 
(1) Position.—In these cases the pollen and the stig- 
ma are ready at the same time; but their position in refer- 
ence to each oth- 
er, or in reference 
to some conforma- 
tion of the flower, 
makes it unlike- 
ly that the pol- 
len will fall upon 
the stigma. The 
three _— following 
illustrations,  se- 
lected from hun- 
dreds, may be 
given: 
In the family 
Fic. 241.—Rose acacia: A, keel projecting from hairy . 
calyx, the other petals having been removed; B, (Leguminose) to 
protrusion of tip of style when keel is depressed ; which th a 
C. section showing position of parts within keel.— e Peay 
After Gray. bean, etc., belong, 
