DEVELOPMENT OF PLANTS 441 



may be lifted off from the convex receptacle like a thimble, while 

 in the blackberries, the drupes remain attached to the receptacle 

 which becomes the most edible portion of the fruit. The at- 

 tractive portion of the strawberry is the enlarged succulent re- 

 ceptacle while the objectionable hard particles on its surface are 

 the akenes. The receptacle surrounds the pistils in the agrimony 

 and rose, but in the former genus it is hard and covered with 

 hooked bristles for distribution of the nut-like fruit, while in the 

 rose it is fleshy and often brightly colored, serving in some cases 

 as food for birds and thus effecting seed distribution (Fig. 313, 

 B, D). The most pronounced changes are seen in the apple and 

 plum families. In the former group, the carpels become tough, 

 forming the "core" (Fig. 314, C) and the edible part is the 

 greatly enlarged receptacle. The plum, cherry, peach, etc., repre- 

 sent the ovary alone, the cup-like portion of the receptacle is 

 cast off as the fruit matures and the ovary becomes a drupe 

 (Fig. 314, F). In the pea family, the ovary usually becomes 

 a pod with elastic valves but it is also variously modified. In 

 the peanut, after the withering of the flower, the pistil is thrust 

 into the ground where it develops as a pod that does not open 

 at all. In other genera, the pod is nut-like as in the clovers, 

 spirally coiled in alfalfa, or separable into nut-like joints that 

 are provided with hooks as in the tick trefoil (Meibomia) (Fig. 

 317, B). Doubtless these methods of distributing their well- 

 developed seeds, their symbiotic relations with the bacteria (page 

 150) and especially the elaborate mechanism of the irregular 

 flowers have been the causes that have led to the abundance and 

 wide distribution of these plants. It will be noticed in the 

 following orders as in the preceding Orchidales, that the irregu- 

 lar and more highly constructed flowers are generally represented 

 by a great number of genera and, barring some weakness, as for 

 example, the poorly developed embryos of the orchids and their 

 peculiar habitats, by a great number of individuals in each 

 species. 



145. Sapindales, the Soapberry Order. — This group includes 

 principally shrubs and trees, as the box, sumac (Rhus), smoke 

 tree (Cotinus), holly (Ilex), burning bush {Euonymus), climb- 



