502 Osborn. — Some Observations on the Tuber of Pkylloglosstim. 
Text-figs. 30-35. Leaves of Series A, detached and put on soil, June 13, 1918. The dates 
below in brackets are those on which the figures were drawn. All x 5J. Fig. 30. Adventitious tuber 
arising from side (Nov. 16). Fig. 31. Extreme case of leaf curvature in vertical plane. Cell mass 
nodular (Sept. 16). Fig. 32 a. Leaf showing vertical curvature. This leaf appears to be an 
exception to rule that adventitious growth occurs from convex surface (Sept. 16). Fig. 32 B. Same, 
viewed from above ; note nodular development of cell mass. This leaf was laid flat on soil Sept. 16 
(Oct. 21). Fig. 32 c. Same; note many short-stalked, white, swollen bodies (Nov. 27). Fig. 33 a. 
Leaf viewed from above, and B, viewed from side, showing geotropic curvature of the many minute, 
stalked tubers (Nov. 27). Fig. 34 A. Leaf viewed from above, and B, viewed from below (Nov. 26). 
Fig- 35 - Portion of leaf, viewed from side, with several scattered centres of adventitious growth. 
Two have developed leaflets and small tubers (Nov. 17). 
Developmental History. 
The first stage in adventitious tuber formation is the development of 
a pad of tissue or cell mass, projecting from the epidermis, at or near the 
proximal end of the detached leaf. This projection is due to the activity 
of certain epidermal cells ; usually several are involved, but it would appear 
