16 AGRICULTURE HANDBOOK 495, U.S. DEPT. OF AGRICULTURE 



PN-4443 



Figure 7. — Tubers of the variety 'Gemelos', somewhat more branched than normal. 



(Two-fifths actual size.) 



adapted to growth in the forest. 

 In nature the relatively leafless 

 new vine climbs rapidly through 

 undergrowth to the tops of trees, 

 where it spreads its foliage. The 

 climbing habit makes it necessary 

 to stake the vines for maximum 

 growth and high tuber production. 

 When vines are not staked, accept- 

 able, but not maximum, yields are 

 sometimes obtained. 



Long rainy seasons are a requi- 



site for optimal growth. Experi- 

 ments have demonstrated that 

 yields are reduced by drought. 

 However, excessive rainfall can 

 contribute to the spread of foliar 

 diseases in susceptible varieties. 

 Furthermore, the plants cannot 

 tolerate excessive moisture around 

 the roots and tubers. 



If drainage is provided, D. alata 

 tolerates a wide range of soil types 

 and pH conditions. Deep, loose, 



