546 SMITH: DIOSCOREA VILLOSA 
ledonous characters indicates that the genus is intermediate be- 
tween the two classes, although he refers it to the Asparageae. 
Endlicher (1836, p. 157) notes a resemblance in stem structure 
between Tamus and Aristolochia. 
Jussieu (1839) finds a structure corresponding to the “second 
cotyledon’? of Dutrochet in the embryos of Dioscorea villosa, D. 
cordifolia, and Rajania hastata. However, he thinks it to be not 
a cotyledon, but a sheath formed by the growth of the cotyledon, 
its development being coincident with the elongation of the 
cotyledonary limb. In his classification the genera in question 
are placed among the Asparageae. 
Beccari (1870a), in agreement with Dutrochet, concludes from 
his examination of the embryos of Dioscorea bonariensis, D. 
brasiliensis, D. sinuosa, Rajania cordifolia, Tamus communis, and 
Trichopus zeylanicus (Trichopodium zeylanicum) that the organ 
in question is a rudimentary cotyledon; he finds it present, with 
some variation in shape and size, in all the species named. Beccari 
also studied the germination of D. bonariensis; his description 
and figure agree substantially with Dutrochet’s account of the 
process in Tamus communis. 
The textbook of Le Maout and Decaisne (1873, p. 794) contains 
a figure of a longitudinal section of a germinating seed of Tamus 
communis, which shows very clearly the structures described by 
Dutrochet and others. 
According to the view advanced by Strasburger (1872, pP- 317: 
318), monocotyledons were derived from dicotyledons by the loss of 
one cotyledon. Obviously, if the Dioscoreaceae can be held to 
constitute a transition stage, or transition stages, between mono- 
cotyledons and dicotyledons, the ‘‘second cotyledon” might well 
represent a stage in the degeneration of one of the cotyledons of 
the latter group. Stimulated by these considerations, Solms- 
Laubach (1878) studied the embryology of Dioscorea pyrenaica and 
Tamus communis, the latter in some detail, but his results did not 
convince him that a second cotyledon was formed. However, he 
found a type of embryological development quite different from 
that which, since the work of Hanstein (1870), had been considered 
characteristic of monocotyledons. The growing point of the 
stem appears early in a terminal or nearly terminal position, 
