352 



A TEXTBOOK OF BOTANY [Ch. VII, 2 



that part which was already most nearly pulp-like in its 

 structure. 



The fleshy fruits thus far described are all simple, that is, 

 composed of a single pistil; but aggregate and multiple 

 fruits also occur. Thus, while in Strawberry 

 the pulp is the receptacle on which stand 

 the many dry akenes, in the nearly related 

 Raspberry the receptacle forms no part of 

 the fruit, which is made up of the many 

 separate aggregate carpels ripened to little 

 drupes ; while in Blackberry both drupelets 

 and receptacle are included. Further, in- 

 stead of a single flower a cluster may form 

 a single large multiple fruit. This is the 

 case in the Mulberry (Fig. 247), in which 

 the pulp is chiefly calyx, and also in the 

 Pineapple, where not only the ovaries, but 

 also the bracts and main stem of a large 

 cluster of flowers ripen to the single coales- 

 cent fruit mass. A different form of 

 multiple fruit is that of the Fig, where the flowers are 

 arranged inside a hollowed receptacle (Fig. 248). Somewhat 

 in the nature of a multiple fruit also is 

 the cone (Fig. 249) of Pines, Spruces, 

 and that family. This form of fruit 

 belongs to the Gymnosperms, or naked- 

 seeded plants, which have no ovaries 

 but usually bear their seeds on the 

 bases of overlapping scales which col- 

 lectively make up the cones. 



The particular feature of pollination 

 which acts as the stimulus to fruit 

 formation is known. The pollen tube, 

 as it reaches the embryo sac (page 278), 

 contains normally two sperm nuclei, of ] 

 which one always fertilizes the egg cell. (From Bailey.) 



Fig. 247. — The 

 Mulberry, made 

 up chiefly of the 

 ripened calyxes of 

 a cluster of flowers ; 

 X \. (From Figu- 

 rier.) 



