328 WALDRON— THE PEANUT 



some slight measure on the downward growth of this organ,geotrop- 

 ism is unquestionably the exciting cause. The writer proved this 

 by inverting two plants which had produced several gynophores 

 whose tips were about to pierce the soil. As seen in Fig. ii the 

 tips turned away and became reversed in position. This not only 

 proved the effect of gravity, but also that the hydrotropic reaction 

 of the organ was weak or lacking. They acted in a similar way even 

 if the soil was saturated. When tips were allowed to penetrate 

 wet sphagnum, and then the plants reversed, they would recurve 

 downward and grow out of it. When the plants were righted again 

 the tips also turned back thus forming an S curve (Plate LXXX,Figs. 

 II and 12). The presence of definite granules in the lumen of each 

 of the epidermal cells of the gynophore (see page 318) at the tip, and 

 their absence anywhere else, suggests the possibility of such being 

 the structures by which this organ perceives when it is out of line 

 with gravity. This has been discussed by others in connection with 

 the presence of starch grains in root tips. The writer found that 

 by cutting off the tip of the gynophore, growth continued, but there 

 was no reaction to gravity when the plant was inverted. The ap- 

 parent homology between the behavior of the root apex and of the 

 gynophore apex is highly suggestive, 



Darwin refers to the means by which this organ penetrates through 

 the soil. He says, "the sharp smooth point of the gynophore en- 

 ables it to penetrate the ground by mere force of growth, but its 

 action is aided by a circumnutating movement." The anatomy of the 

 organ is also suggestive. The patches of hard bast give strength, 

 while their separation, even though in a close ring, gives pliability. 

 Pettit states that the hairs produced at the tip are also an aid in 

 holding it firmly. Although this happens to be of some assistance, 

 the writer would question to what extent, since the relation of the 

 radicle to soil penetration puts a new light on this matter. Hair 

 experiments, similar to those of Pettit, were made with plants bear- 

 ing young gynophores, which had not yet reached the soil. Pettit 

 found that by putting these in a moist chamber a narrow zone, 

 averaging 3 mm. in length, always appears one to eight millimeters 

 from the tip. The writer found by repeated experiments that this 

 zone might be as much as 5 cm in length (Plate LXXX, Fig. 13). 



In discussing these in relation to those of roots, Pettit says: "In 

 comparing the growth of gynophore hairs with that of root hairs it 

 must be remembered that the growing point of the gynophore cor- 



