306 PLANT LIFE. 



carpels of a single flower. Compare the multiple fruit of the 

 mulberry (each section from a separate flower whose floral 

 leaves and pistil both become pulp}-; fig. 356) with such an 

 aggregate fruit as the blackberry, in which each section is 

 one pistil out of the many belonging to a separate flower (fig. 

 355). The pineapple is similar to the mulberry in origin. 



Even more remote parts are stimulated to development by 

 fertilization of the egg. The stem bearing the flower gen- 

 erally grows and becomes stronger, to carry the fruit, espe- 

 cially if large. The minute bractlets sometimes become 

 highly developed beneath the fruit. The cup of the acorn 

 and the husk of the hazelnut originate in this way as the 

 nuts form. The similar husk of the beechnut and chestnut 

 encloses more than one fruit. 



414. Distributive arrangements. — Since the seed plants 

 abandoned the distribution of the megaspores and form both 

 the gametophyte and the new sporophyte within the tissues 

 of the old, it became necessary to adopt some other method 

 whereby the young can be so scattered as to prevent them 

 from coming into sharp competition with the parents. This 

 distribution occurs at the time of maturity of the seed, i.e., 

 when the embryo has become dormant, and the food store 

 and protective coverings have been completed. The devices 

 by which seeds are scattered are dependent upon the number 

 and character of the seeds and the nature of the pericarp. 

 Thus, one-seeded, indehiscent fruits must be scattered by the 

 structures arising upon the surface of the pericarp or its ad- 

 herent parts. On the contrary, seeds which escape from the 

 pericarp have the distributive structures developed by the 

 seed coats themselves. For distribution plants adapt them- 

 selves so as to employ the agency of the wind, water, and 

 animals, or they develop special mechanisms for casting off 

 the seed as a projectile. A consideration of these adapta- 

 tions belongs to ecology. (See Chap. XXVI.) 



