456 SAPINDALES 



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., rep- 

 resent 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 distribution, the well- 

 developed seeds with their exceptionally firm integuments, the 

 symbiotic relation of these plants with the bacteria (page 161) 

 and the elaborate mechanism of the iregular 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 irregular 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), cHmb- 

 ing bittersweet (Celastrus), maple (Acer), horse-chestnut and 



