500 Dale . — Origin , Development , and Morphological 
elevations which mark the position of adventitious roots. 
The plant described by Queva as Helmia bulbifera , Kunth, 
appears to be the one which was considered above to be 
identical with Dioscorea sativa, Linn., i. e. the species under 
consideration in this paper. This opinion is confirmed by 
a comparison of the development of the tubers as described 
by Queva and by the present writer. The descriptions may 
be briefly compared in some points. Queva observes that 
the growing points of the original buds (usually three) remain 
in the plane of symmetry of the organ, which corresponds 
with that of the leaf. On the mature tuber the growing 
point of the posterior bud is placed on the lower surface, that 
of the middle bud on the upper side, while the anterior bud 
remains near the point of attachment of the tuber. The 
observations made on the tubers grown at Cambridge show 
that in large tubers the three buds lose their original positions 
and all come to lie close to the point of attachment. They 
are therefore all on one side of the tuber in an advantageous 
position when they begin to grow. Adventitious buds are 
also formed, close to the original buds. 
The abundant formation of axillary tubers in many species 
of Dioscorea seems as if it were connected with the fact that 
these plants do not appear to form seed readily. The experi- 
ments with the plants grown without water in the laboratory 
show that the tubers, and the shoots which they produce, 
have a great power of resisting drought, which would often 
kill the more delicate tissues of a seedling. Vegetative re- 
production by means of axillary tubers appears to a large 
extent to have superseded sexual reproduction in this genus. 
In conclusion I wish to thank Professor Marshall Ward for 
allowing me to work in the University Botanical Laboratory, 
and for the help which he always so willingly gives. 
