Tin Txcs of Texas 13 



ing. It is the device by which perpetuation is. insured. The chief 

 problem of each organism that lives is to maintain its existence 

 during life and to leave others like itself when it dies. The 

 flower then is the structure upon which the perpetuation of the 

 species depends and toward which all the energy of the tree is 

 directed. The mightiest trees which today inhabit the earth 

 began life, some of them, perhaps eight thousand years or more 

 ago, when the pollen tube delivered its sperm cell to the egg cell 

 in the young ovule. For in this way, and this way only, can a 

 new individual originate. 



The transfer of pollen from the anther to the stigma is known 

 as pollination. When the pollen is borne on one flower and the 

 stigma on another, the process is known as cross-pollination; but 

 if they are produced in the same flower it is called self or close 

 pollination. Perhaps the great majority of plants favor cross- 

 pollination, for there are many evidences in support of this 

 theory. In many plants the flowers are incomplete; that is r 

 some flowers bear only stamens while others bear only pistils y 

 and in some plants these two types are borne on separate indi- 

 viduals. Such plants are called dioecious. 



Cross-pollination is brought about through the agency of the 

 wind, water and insects. Wind pollenized flowers are usually 

 small, consisting only of the essential flower parts, while those 

 which are visited by insects are usually larger, more showy and 

 produce nectar and odor. The relationship which exists between 

 insects and flowers is one of the most interesting chapters in 

 biology. The insect and the flower have evolved together, and 

 they perform for each other a mutual service. The insect visits 

 the flower in order to procure food, but while there its body be- 

 comes dusted with pollen, and this is transferred to other flowers 

 which it then visits. The pollen of one species will grow only 

 upon the stigma of the same or of a closely related species. This 

 tends to keep each species pure. However, crossing may occur 

 provided the pollen of one species is carried to the stigma of an- 

 other that is closely related to it. This has led to the improve- 

 ment of many of our cultivated varieties of plants as well as to 

 the origin of entirely new hybrid varieties. 



Flowers are either borne singly on the stem or in clusters. 

 When the flowers are solitary, they are either on short lateral 



