324 WALDRON— THE PEANUT 



water, and as a result rosette hairs were the only type observed. 

 These were absent on the roots furthest from the moist cotton. 



Concerning the function of root hairs on the radicles of seedlings, 

 Haberlandt and others state that one reason for their early forma- 

 tion on these, is, that the main root may have sufficient anchorage 

 in order to rapidly penetrate the soil for its immediate needs. Evi- 

 dence presented by the peanut thus entirely contradicts such a 

 view, indicating that they are not necessary for this purpose. Such 

 seeds as those of the peanut can alone supply adequate food material 

 for germination if water is present. The radicle elongates and pene- 

 trates a light soil with great rapidity without them. This may be 

 one reason why a light sandy soil is best for this species. This 

 thought also suggests an interesting relation to the hypogeal fruit 

 production. The plant always maturing its seed under ground 

 would not need such anchorage for its first root growth, 

 even though it were a desirable feature. The fruit wall acts also 

 as an aid. The writer feels, however, that the reason why hairs 

 are not present here is that the outer layers, in stripping off (see 

 page 314), do not allow their development. The fact that side 

 roots, which do not show this peeling, will form them under proper 

 stimuli is evidence of this. Even these do not often produce them, 

 probably because of their very loose structure (see page 314). The 

 cells which are best adapted to respond are at the base of side roots, 

 thus rosettes are formed. 



To summarize these observations, the results of the root hair 

 experiments on the peanut indicate that (i) light and darkness have 

 no effect on their production; (2) high temperature, with sufficient 

 moisture and air, accelerate the growth and production of the rosette 

 type; (3) loose sandy soil, with root aeration, stimulates hair growth 

 on the tips of young plants, and possibly also on old plants, if a 

 period of retardation is followed by a suddenly renewed root vigor. 

 The rosettes of hairs may appear on any plant of more than one to 

 two weeks' growth. The tip hairs are found only on young roots 

 that are undergoing a vigorous elongation in a natural or artificial 

 moist air space at a high temperature. Low temperature, lack of 

 oxygen and wet heavy soil prevent the normal tip type from appear- 

 ing and retard the rosette form. None appear on the radicle. The 

 cause for the production of the rosette hairs at and on the base of 

 the side roots is hard to explain. It may be that, at the time the 

 side root is penetrating the cortex and epidermis of the main root. 



