286 



' LESSOIf^S WITS PLANTS 



there is difference of opinion as to its morphol- 

 ogy. The walnuts and hickories are somewhat 

 closely allied to the oaks, and it is held by 



some that this husk is 

 an involucre, although it 

 has none of the obvi- 

 ous features (as scales) 

 of an involucre. Others 

 regard the flask -like body 

 as a calyx -tube, and 

 the four sepal -like parts 

 as calyx lobes. In the 

 hickory, the petals are 

 wanting (Fig. 160), but 

 the charactetristics of the 

 calyx -cup are very simi- 

 lar. These two fruits show what a specialized 

 feature dehiscence or indehiscence is ; and they 

 are particularly interesting as showing how much 

 our interpretation of particular structures depends 

 upon comparatively minor features. 



337. The chestnut will now interest us. A 

 mature bur is at Fig. 293. In this case there are 

 two or more pistillate flowers (each with a well 

 marked calyx) aggregated in a scaly and prickly 

 involucre. Does one chestnut develop from each 

 single flower? This involucre grows with the nuts, 

 and becomes the 4-valved bur shOAvn in the picture. 



Fig. 292. 

 Pistillate flowers of butternut. 



