MORPHOLOGY, GENETICS AND BREEDING 29 



interpretations of 1839 are still to be found in many recent textbooks. 



Beginning with a consideration of the peanut seed and seedling and 

 passing to the mature root, stem and leaf, this chapter then deals with 

 the reproductive morphology of the plant and concludes with a discus- 

 sion of its genetics and breeding. Without attempting to cite all the 

 known references which have some bearing on the topics discussed, the 

 writers have attempted to cover the topics themselves with as much 

 thoroughness as existing knowledge permits. This chapter does not in 

 any sense represent a botanical or genetic monograph on the genus 

 Arachis but does summarize botanical and genetic information as it re- 

 lates to a single species of the genus. It is our purpose to present the 

 status of knowledge on peanut morphology, reproduction, variation, and 

 breeding. 



SEED AND SEEDLING 



Outstanding features of the seeds of cultivated peanuts are their 

 variable sizes, colors, and shapes. They may be red, white, purple, pink, 

 flesh, rose, tan, light brown, or even red and white. The actual range of 

 seed size in peanuts is probably unknown, but we have seen and planted 

 seed ranging from 0.2 of a gram to 10 times that size. Seeds may be 

 almost spherical, elliptical or much elongated. 



Each seed is composed of two massive seed leaves (cotyledons) , upper 

 stem axis and young foliage leaves (epicotyl), and lower stem axis and 

 primary root (radicle). A thin papery seed coat covers the seed (figure 

 1). In contrast to most papilionaceous legumes the axis of the embryo 

 proper is straight. All of the leaves and above-ground parts which the 

 seedling will have for the first 2 to 3 weeks of growth are already present 

 in the dormant seed. The epicotyl consists of three buds, one terminal and 

 two cotyledonary laterals. In the terminal bud there are four foliage 

 leaves and in the cotyledonary laterals one or two leaves. Thus the dor- 

 mant embryo has from six to eight differentiated leaves, all of them 

 ready to expand and go to work immediately upon germination (76). 



When peanut seeds are put to germinate at 80 °F. the radicle appears 

 after 24-36 hours. Reporting from Senegal, Bouffil (13) stated that 

 hardly 2 days elapse before the appearance of the radicle. In Germany 

 Richter (59) found that 8 to 10 days were required for germination in 

 damp sphagnum in the hothouse. In outdoor plots at Raleigh, North 

 Carolina, 8 to 10 days were required for emergence. Discrepancy be- 

 tween the appearance of the young root (24 to 48 hours) and the ap- 

 pearance of the shoot (8 to 10 days) is caused by a striking difference in 



