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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 1 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 

 (Leguminosce) to 

 which the pea, 

 bean, etc., belong, 



Fia. 241 . Rose aeacia : A , keel projecting from hairy 

 calyx, the other petals having been removed; B, 

 protrusion of tip of style when keel is depressed ; 

 C. section showing position of parts within keel. 

 After GRAY. 



