52 THE PEANUT— THE UNPREDICTABLE LEGUME 



"the young fruit during the stalk-like phases of development which inter- 

 vene between syngamy and fruit enlargement." Smith has shown that this 

 stalk-likeorgan is^not a gynophore_but in. reality the ovary, elongated by 

 the growtli of an intercalary meristem in its base. Jacobs (39) has de- 

 scribed the development of this meristem and the differentiation of the 

 tissues arising from it. He has shown that the vascular strands extend 

 through the meristematic region to the base of the ovarian cavity. The 

 loculus of the ovary, distal to meristem in the tip of the peg, contains 

 the 2 to 6 ovules. 



The ovary is enclosed by cataphylls of the inflorescence, which in 

 turn are covered by the stipules of the subtending leaf. Peg growth be- 

 gins immediately after fertilization and the peg usually appears from 

 within the enclosing bracts and stipules several days after anthesis. Early 

 growth is slow but gradually accelerates until the pegs are elongating very 

 rapidly. 



The peg is positively geotropic. Charles Darwin (21) showed in 

 1880 that the peg was not negatively phototropic but did respond to the 

 force of gravity. The later observations of Badami (3), Jacobs (39), 

 Shibuya (65), Theune (71) and Waldron (75) have supported this 

 view. The ultimate length of a peg and the time required for it to reach 

 the soil is determined by the initial distance from the ground. Pegs in- 

 serted more than 15 cm. above the soil surface usually fail to reach the 

 ground. In such circumstances, the peg tips usually fail to reach the 

 ground. In such circumstances, the peg tips usually die and pod and seed 

 development do not occur. Exceptionally, ovule enlargement does occur 

 and viable seed develop in aerial pegs, but normal pods are not formed 

 ( Gregory in Smith, 66) . 



Upon penetrating the soil the peg commonly grows to a depth of 2 

 to 7 cm. (but may be covered much deeper than this by cultivation). For 

 several centimeters immediately above the soil surface the peg sometimes 

 becomes fleshy and much thickened, and loses its green or purple color. 

 Its lenticels become enlarged and irregular. Many multicellular hairs may 

 be found on the peg surface. Underground the peg may become similarly 

 expanded and have copious hairs. The function of these hairs is proble- 

 matical. Pettit (50) and Waldron (75) have interpreted the hairs of the 

 peg and pod as "root hairs" in structure and function, but Richter (59) 

 found their cell walls suberized. He suggested that they anchored the 

 peg in the soil. These ha irs are not root hairs but are multicellular 

 trichomes characteristic of stems. 



