Nature of aerial Tubers in Dioscorea sativa, Linn. 499 
with two series of cicatrices which result from the annual 
detachment of the stem and root respectively. 
Bucherer 1 points out that the tuber of D. Batatas has the 
structure of a root. 
Only one author, Morot 2 , appears to hold that these under- 
ground tubers are stems. He regards each of them as con- 
sisting of a single reduced internode. In this way he explains 
the absence of scales. 
The majority of tubers in the Dioscoreaceae are, however, 
undoubtedly stem-structures. They are considered to be 
rhizomes in D. bulbifera and D. pentaphylla 3 and, as already 
mentioned, in D. villosa. In D. aculeata 3 short stolons bear, 
at their distal ends, rounded tubers about the size of the fist. 
One plant bears as many as seven or eight 4 . 
The tuber is in. some species the first internode of the stem, 
and is therefore leafless, e. g. Tamils , Testudinaria , and some 
species of Dioscorea. According to von Mohl 5 , the tuber of 
Tamas (Testudinaria) Elephantipes is to be regarded as an 
adventitious bud, which each year is formed anew between 
the wood and the cortex of the tuber-like stem. Consequently 
the annual shoots are developed from adventitious buds. 
The axillary tubers are, in all cases, stem-structures, the 
only question being as to the number and nature of the buds 
which occur upon them. Such aerial tubers are formed on 
many species ; their development has been described in 
D. Batatas, Decsne, and Helmia bulbifera , Kunth, by Queva 6 . 
In D. Batatas the tuber arises as a single axillary bud. 
There are in each axil also one or two other buds which 
are branches. The surface of the tuber is covered with slight 
1 Bucherer, Beitrage zur Morphologie und Anatomie der Dioscoreaceen. Bot. 
Centr., vol. xliii, p. 121 (’90). 
a Morot ; see Royer, 1. c., p. 227. 
3 Vieillard, Plantes utiles de la Nouvelle Caledonie. Ann. des Sci. Nat., 4® ser., 
vol. xvi, pp. 39-40 (’62). 
4 Sagot, Des Ignames. Bull, de la Soc. Bot. de France, vol. xviii, p. 309 (’71). 
5 Von Mohl, Untersuchungen liber den Mittelstock von Tamus Elephantipes , L. 
Verm. Schrift. Bot. Inhalts, p. 193 (’36). 
6 Queva, Les Bulbilles des Dioscorees. Comptes Rendus des Seances de l’Acad. 
des Sciences, vol. cxvii, pp. 316-318 (’93). 
L 1 
