208 GROWTH AND WORK OF PLANTS 



a crown of leaves (involucre) at the base of the flower grows 

 around the nut and completely envelops it, forming the husk 

 or burr. When the fruit is ripe the nut is easily shelled out from 

 the husk. In the beechnut and chestnut the burr dehisces 

 as it dries and allows the nut to drop out. But the fruit is not 

 dehiscent, since the pericarp is still intact and encloses the seed. 

 3. The hickory nut, walnut, and butternut. In these 

 fruits the "shuck" of the hickory nut and the "hull" of the 

 walnut and butternut are different from the involucre of the acorn 

 or hazelnut, etc. In the hickory nut the "shuck" probably 

 consists partly of calyx and partly of involucral bracts consoli- 

 dated, probably the calyx part predominating. This part of the 

 fruit splits open as it dries and frees the "nut," the pericarp being 

 very hard and indehiscent. In the walnut and butternut the 

 "hull" is probably of like origin as the "shuck" of the hickory 

 nut, but it does not split open as it ripens. It remains fleshy. 

 The walnut and butternut are often called drupes or stone- 

 fruits, but the fleshy part of the fruit is not of the same origin 

 as the fleshy part of the true drupes, like the cherryj peach, 

 plum, etc. 



HI. DEHISCENT FRUITS. 



The dry dehiscent fruits are pods, but several prominent 

 types are recognized. 



331 . The capsule. The capsule is a dry dehiscent fruit of two or more 

 carpels (compound pistil). It may dehisce in three different ways: ist. 



Fig. 160. 



Diagrams illustrating three tynes (in cross section) of the dehiscence of dry fruits. 

 Loculicidal; Sep, Septicidal, Septifragal. 



The carpels split along the line of their union with each other longitudinally, 

 as in the azalea or rhododendron. 2d. The carpels split down the middle 

 line, as in the fruit of the iris, lily, etc. 3d. The carpels open by pores, as in 

 the poppy. Some capsules have but one locule, the partitions between the 



