The Growth of Fruits, Seeds and Embryos. 73 



Often, particularly in dry countries, branches or leaves 

 become protective spines. In our hookeras (Fig. 64) the 

 three sterile stamens (staniinodia) put their heads together 

 for the purpose, probably, of keeping out intruders, as well 

 as to insure the economical collection and transference of 

 pollen. In many cultivated plants stamens no longer neces- 

 sary for the production of pollen cease to attempt usefulness 

 in that way and develop into beautiful petals to please man.* 

 Questions That Should be Considered in the Discussion. 

 What parts of a flower are modifications of the stem ? 

 Which of the four kinds of leaf parts are most modified or 

 changed from the ordinary leaf form and nature t Which 

 are the least changed ? How does a nasturtium leaf do the 

 work of a tendril ? What materials are stored in a beet ? 

 In a potato ? What harm would be done by ordinary leaves 

 in place of the bracts in a bunch of lilac blossoms? Is a 

 spine doing a lower work than a leaf? Explain how man 

 can change the organs of a flower or the character of fruit ? 



EXERCISE 41. 



[Read and discuss in the class. ~\ 



The Growth of Fruits, Seeds and Embryos. The 



development of fruit from the ovary is often very interest- 



* Man is, perhaps, the only animal excepting insects, and a few birds, that 

 has had any influence upon the arrangement, size, form, color, and odor of 

 flowers. Doubtless the present condition of many wild fruits was brought about 

 by the higher animals. Man, beginning where these animals left off, has greatly 

 modified the fruits of plants which he cultivates. 



Some plants would long ago have become extinct had it not been for man. 

 Indian corn and wheat, for example, are not known in a wild state. 



