TROPICAL YAMS AND THEIR POTENTIAL, PART 3 



7 



which develop rapidly after polli- 

 nation, reach 20 to 30 millimeters 

 in length. They mature, dry, and 

 split along the sutures of the wings 

 to release two seeds from each of 

 the three locules. Few capsules are 

 produced, however, even when 

 male and female plants are grown 

 together. Moreover, the develop- 

 ing capsules often contain only a 

 single seed, and this frequently 

 aborts before maturity. Thus, as 

 in the case of males, most female 

 plants are sterile. The author has 

 no experience growing D. alata 

 from seeds and believes that con- 

 ventional breeding of this species 

 would be extremely difficult. 



Only newly germinated seeds 

 have true roots; the roots of de- 



veloping tubers are strictly ad- 

 ventitious, the tuber being nodeless 

 and originating from the stem. The 

 principal roots arise from what is 

 sometimes called the primary 

 nodal complex (fig. 3), or crown, 

 of the plant, near the surface of the 

 ground, but in some varieties, a 

 variable number of roots arise 

 from the body of the tuber itself. 

 When stems touch moist soil they 

 often develop adventitious roots 

 and may even develop large tubers. 



The tubers of D. alata are ex- 

 tremely variable, and the number 

 of possible forms almost endless. 

 Plants normally bear only one 

 tuber, but two to five are common, 

 even on varieties typically produc- 

 ing one tuber. These are normally 



, PN-4439 



Figure 3. — Primary nodal complex of rooted cutting of D. alata, showing origin 

 of roots and shoots. (Three times actual size.) 



