COLOR IN PLANTS 153 



produce a seed which will grow and give rise to a new 

 plant, pollen from a stamen must be deposited on the 

 stigma, or tip of the pistil ; here it will sprout and send 

 down a tube within the pistil to reach and fertilize an 

 ovule (Fig. 44, ?, j, and 5), which then becomes a seed 

 capable of producing a new plant. Now, it has been 

 observed over and over ao-aiii that if a pistil is impreo-- 



O J. O 



nated with pollen from another plant the new plants com- 

 ing from the seeds thus fertilized will often be stronger 

 and more vigorous than if they had been developed from 

 seeds fertilized by pollen from the same plant that formed 

 the seeds. Cross-fertilization, as it is called, is advanta- 

 geous. Self-fertilization does occur, but it is important for 

 most species that cross-fertilization should come in every 

 few generations at least. 



Different methods of fertilization are adopted by differ- 

 ent kinds of plants. The tiow-erless plants have their own 

 methods, and the flowering plants usually different ones. 

 \Ye are here interested only in the means of securing fer- 

 tilization adopted by the flowering plants. Some of these, 

 like the pines and other evergreen trees, have an enormous 

 amount of pollen which is cast out into the air in great 

 clouds and is carried by the winds to the female cones, 

 there to fertilize the ovules (Plate 87, A}. There are many 

 such wind-fertilized plants, the palms and grasses, as well 

 as the cone-bearing trees, being familiar examples. These 

 do not use insects to aid in carrying pollen to fertilize 

 their ovules, and so, as every one knows, they have no 

 brilliantly colored blossoms (Plate 87, B}. 



By far the larger number, however, of our common 

 flowering plants are aided in securing fertilization by the 



