314 WALDRON— THE PEANUT 



and semi-transparent. Placing a portion of one on a slide for exam- 

 ination under the microscope must be done with care, for the epider- 

 mal and outer cortex cells seem readily to fall apart like so many 

 poorly cemented bricks becoming loosened. This is due, in part at 

 least, to pressure from within, since, as noted by Pettit, the inner 

 meristems develop much faster than the dermatogen. This is mark- 

 edly evident on the primary root where the surface cells are continu- 

 ally peeling off in rows or patches. Sufficient protection, according 

 to Pettit, is afforded by a cutinized outer wall being formed by the 

 cells which become exposed. Pettit also states that the lateral 

 roots act in a similar way, but the present writer did not find this to 

 be the case with his plants. These roots are always normal in this 

 regard, although very delicate. As they increase in age, their outer 

 surface is supplied with a regular periderm, and it is only in the 

 early stages of radicle growth that this peculiar habit is observed. 



Stem 



The stem is normal for dicotyledons. The epidermis is composed 

 of a layer of small, thickly cuticularized cells interrupted by stomata 

 in young stems and by a corky lenticel proliferation in old ones. 

 Three-celled hairs are scattered along young stems. These are 

 typical of many other Legiminosae, each hair having a long pointed 

 terminal cell with two tiny, flattened basal cells. There are also 

 small crystal cells arranged in groups of two to four, each containing 

 one rectangular crystal. The cortex is six to eight layered and com- 

 posed of much larger thin walled cells. At the outer extremity of 

 the primary bundle areas of the vascular system are large patches 

 of highly indurated hard bast. This, along with the quite extensive 

 and considerably indurated xylem, give a tough and flexible char- 

 acter to the stem. The pith in young stems is composed of round 

 extremely thin walled cells filled with starch. As the stem matures, 

 however, the pith becomes more or less broken down resulting in a 

 semi-hollow condition. Concerning the cambium, a very interesting 

 relation is noted later as to its development in the fruit stalk (see 

 page 314). 



Leaf 



The leaf structure of the peanut is most striking, especially when 

 the xerophytic tendencies of the plant are considered. There are 

 numerous average-sized stomata on both surfaces that are neither 



