JOURNAL 



OF THE 



ASIATIC SOCIETY OF BENGAL, 



Vol. LXXIII. Part II.— NATURAL SCIENCE, 



Supplement— 1904 



On Dioscorea deltoidea^ Wall., Dioscorea qiiinqueloha, Thunb., and 

 their allies. — By D. Prain and I. H. Burkill. 



In the following paper we describe eleven species of Dioscorea — 

 three Indian, three Chinese, and five Japanese. They are all allied 

 plants, with many characters in common : and as it may perhaps con- 

 duce to clearness we give the common characters as a preliminary. 



Characters which these Yams have in common. 



I. Tubers as far as known inedible, not lying deep in the soil, at times 

 growing like rhizomes pai'allel with the surface. 

 II. Stems always twining to the left. 

 III. Leaves cordate (or truncate below), constricted more or leas towards the 



middle, or else lobed, with 5-9 palmately arranged nerves. 

 IV. Male flowers generally two or more together. 

 V. Female spikes pendulous, with recurved fruit. 

 VI. Wings of capsules with a tendency to be quadrate. 

 VII. Seeds winged all round but irregularly so, ai^parently distributed as 

 from swinging censers by the movement of the flexuous slender spikes 

 in the wind. 



The species group themselves naturally in a way that more or less 

 accords with their distribufciou. The first little group contains four, — 

 J. II. 1 



