38 THE PEANUT— THE UNPREDICTABLE LEGUME 



always underground and the stele is surrounded by a fleshy cortex. In 

 the dormant seed most of the radicle is actually hypocotyl tissue and is 

 filled with stored food. During germination the hypocotyl, cortex, and 

 pith may serve as way-station, storage tissues for food moving out of the 

 cotyledons to the roots. 



The hypocotyl, when cut transversely (figure 6), shows an intact epi- 

 dermis covered by a thin cuticle, a wide cortex where much stored food 

 may be found, and a central stele in which the conducting tissues, xylem 

 and phloem, are arranged on the collateral plan. The vascular bundles of 

 the hypocotyl increase to nine or more as compared to four in the root and 

 surround a large pith. As the hypocotyl becomes older ( 10 to 30 days) it 

 undergoes two significant changes, the first of which is a collapse of 

 epidermis and much of the cortex. The collapsing layer becomes soft and 

 may be easily rubbed off. Secondly, the collar at the base of the hypocotyl 

 becomes very woody and hard. The pith breaks down and the hypocotyl 

 ultimately becomes a hollow woody axis (76). 



COTYLEDONS 



The position of the cotyledons during germination determines whether 

 a seedling is classified as epigeal, i.e., with its cotyledons above the sur- 

 face of the ground as in the green bean or the soybean, or hypogeal as 

 in the case of the garden or English pea. In the first case the growth of 

 the hypocotyl pushes the cotyledons upward until they appear above the 

 surface of the soil. In the latter case the cotyledons remain just where 

 the seed was placed when planted. Peanuts do neither. The cotyledons 

 rise with the hypocotyl' until the soil surface is reached and there they 

 stop. Bouffil (13) said that they were hypogeal; Yarbrough (76) said 

 that they were not epigeal.. This growth of the hypocotyl which de- 

 termines the position of the cotyledons is a function of the depth of plant- 

 ing. Bouffil planted seeds of peanuts at depths of 3, 6, and 9 cm., and 

 found that the position of the planted seed determined the position of the 

 collar, and that the length of the hypocotyl was clearly related to depth 

 of planting. Yarbrough (76) has made a similar statement about hypo- 

 cotyl length. This fact is strikingly borne out in seedlings volunteering 

 in newly ploughed fields in the spring following a crop of peanuts the 

 previous summer. Many of these peanuts germinate on the plough sole 

 and sometimes must rise 12-14 cm. before reaching the surface. Under 

 these conditions the entire food supply from the cotyledons may be 

 exhausted and the young epicotyls emerge pale and yellow. When this 

 happens it has been consistently noted that with increasing depth of 



