84 MacDougaL — The Water-balance of Desert Plants . 
comparative examination was made of this material with stems of vines 
in the conservatories and of the young stems sent out by tubers in the 
propagating houses. The work of Duchartre upon D. Batatas , Dcsne., 
was found of great interest in connexion. 1 Duchartre placed tubercles 
in a dry chamber where they would be compelled to sprout without a- 
supply of soil moisture, in a manner similar to that noted above. He 
noted that the stems developed were 50 to 80 cm. long, composed of 
elongated internodes, and that the leaves remained extremely small with 
diminutive laminae, entirely lacking from lower internodes, and showed 
a lack of mechanical tissues, from which he points out the resemblances 
to etiolation as exhibited by some plants. The bases of the stems re- 
mained green, but the remainder of the epidermal structures were of a 
reddish brown colour. He also noted that the base of the stem became 
the seat of the formation of a tuberous swelling which must have been 
the beginning of the large tuber usually formed by these plants under- 
ground. No stomata were found on the reduced leaves, the starch was 
not all converted, and the unequal thickenings were not seen in the layer 
of cells usually becoming collenchymatous. (See PI. IX, A and B.) 
Miss Dale performed similar cultural experiments with Dioscorea 
satwa } although no reference is made by her to the previous experiments 
of Duchartre. 2 
In this case also elongated stems were formed which measured as 
much as six or eight feet. The formation of buds at the bases of the stems 
was noted, but no comparisons of the lengths of internodes with those of 
the normal were made. Tuberous structures were seen to develop in the 
axils of the leaves, and the branches remained very short. The formation 
of adventitious roots around the bases of the stems, with a scaly epidermis, 
was noted. 
The stems in my cultures of D. alata did not seem capable of 
reaching the lengths described by Duchartre and by Dale in the two 
species named, but this deficiency may be accounted for in part by the 
smallness of the tubers and correspondingly small supply of food-material 
available. The stems consisted of two to five internodes, and were angular, 
reddish brown, and bore numbers of trichomes and glandular structures. 
The internodes were of a length less than that of the normal in every 
instance. The bases of the stems underwent a tuberous swelling from 
which arose numbers of short thick adventitious roots (PI. IX, c). 
The leaves were extremely small, and were in the form of narrow 
reddish brown scales, with no differentiation into lamina and petiole. The 
axillary buds showed an activity similar to that of the main buds of the 
1 Duchartre, P. : Influence de la secheresse sur la vegetation et la structure de l’igname de Chine 
Dioscorea Batatas , Dcsne. Bull. Soc. Bot. de France, vol. xxxii, 1885, p. 156. 
2 Dale, E. : On the Origin, Development, and Morphological Nature of the Aerial Tubers in 
Dioscorea sativa, Linn. Ann. of Bot., vol. xv, 1901, p. 491. 
