Nature of aerial Tubers in Dioscorea saliva , Linn. 497 
nodes tubers were not formed, though they were developed 
at all the* free nodes. 
When the plant died down in the autumn a new under- 
ground tuber had been formed at the base of the annual 
stem, of smaller size than the original axillary one, which 
had been emptied of its contents but still remained attached 
to the stem (Fig. 6). The new tuber was covered with roots, 
which were arranged in more or less definite rings on its 
surface, as is the case also in the undeveloped roots of the 
axillary tubers (cf. Figs. 3 and 6). 
The axillary tubers of another species of Dioscorea , perhaps 
D. divaricata , behaved differently when planted. This species 
grows out of doors at the Botanic Garden, and in the autumn 
it produces numerous small tubers which are about the size 
of peas, either rather smaller or a little larger. Usually there 
is only one in the axil of each leaf, but there may be two 
or even three. As in D. sativa, they possess both buds and 
roots. In both species the structure is similar. When one 
of these little tubers is planted it sends up one shoot, and 
begins itself (Fig. 7) to grow downwards as an elongated 
mass, while at the same time it forms, like D. sativa , a com- 
paratively large new tuber, often of irregular shape. 
Some interesting points were noted in tubers which formed 
shoots in the laboratory, without water, but in the presence 
of light. In two cases a single stem, six or eight feet long, 
was produced by each tuber, while from two other points 
smaller shoots were formed. It is noteworthy that “at the 
bases of these stems buds were formed, which must be 
adventitious. Although the stems were so long and were 
also comparatively thick, the leaves were scarcely developed 
at all, and the axillary branches remained small (Figs. 3 and 4). 
Nevertheless, small tubers about half an inch in diameter 
were formed in the axils of most of these arrested leaves. 
The number and arrangement of the buds on these tubers 
and in the leaf-axils which bore them have been described 
above (p. 495). Round the bases of all the shoots numerous 
adventitious roots were formed, some of which became about 
