are basifixed on short, slightly connate filaments and are com- 

 posed of two thecae dehiscing in extrorse and introrse fashion. 

 The highly vacuolated pollen grains are small and sticky, which 

 makes pollination by wind impossible. 



Female flowers are seen infrequently in D. rotundata and 

 even less seldom in D. cayenensis, a consequence of the complex 

 determining mechanism that results in more males than females. 

 Female flowers occur on axillary spikes and are about 0.5 centi- 

 meter long. The perianth consists of two whorls of three sepals 

 and three petals, which are lobed over the ovary. The pistil is 

 single, with a trifurcated stigma. Two to three staminodes are 

 sometimes present and are located peripherally to the style. The 

 ovarj^ is inferior and trilocular, with each locule containing two 

 ovules. Upon maturation, the perianth dries out while the ovary 

 continues its development into a capsule, which opens vertically 

 and releases up to six seeds with thin leathery wings that help in 

 seed dispersal. 



The tubers of both species are much less variable than those 

 of D. alata. They are most commonly cylindrical and seldom 

 branched (fig. 5). On encountering an obstacle a tuber may de- 

 velop a foot, lumps, or appendages. The tuber skin, being thick and 

 corrugated, provides good protection in storage. The size of the 

 tuber varies from less than 200 grams in wild types to about 25 

 kilograms in cultivated varieties. 



The flesh of the D. rotundata tuber is white and because of 

 the presence of vascular bundles around which starch deposits are 



PN-5219 



Figure 5. — A collection of D. rotundata tubers in Ghana. 



8 



