ADHESIVE DISCS OF ERCILLA VOLUBILIS. 101 
be carried over them when rain falls on to the lamina. Beyond 
this coincidence, however, there is no evidence of absorption on 
the part of the disces, and indeed the presence of the cork renders 
it impossible in the older ones. 
Summary.—The results arrived at may be briefly summarized 
as follows :—The adhesive organs are developed endogenously 
immediately above the axils of the leaves. Each is made up of 
a mass of parenchy ma, with a central plate of tracheides, in con- 
uexion with the bundles of the stem at the base of the disc. 
Hairs, which force their way into the crevices of the support, 
are formed from a special layer of columnar cells beneath the 
epidermis, resulting in the exfoliation of the latter. After a 
time the walls of the cells in the external layers of the discs 
become suberized, a periderm being eventually formed from a 
definite cambium just outside the vascular plate. While abso- 
lute contact is necessary for complete development, dises of 
various sizes may occur some distance from the support, possibly 
stimulated to growth by a moist environment. <A few dises give 
rise to small roots, but, as the walls of the cortical cells are 
luvariably suberized, they cannot function in a normal manner. 
While there is no evidence to indicate that the discs function 
other than as climbing organs, at the same time a comparison 
with parasitic organs, such as those of Cuscuta, suggests the 
possibility that the dises are not far removed from acting 
parasitically. 
I have to thank the Council of the Royal College of Science, 
South Kensington, for granting me the use of a table in the 
Huxley Research Laboratory, where this work was completed. 
I am also indebted to Professor Bayley Balfour for suggesting 
the investigation, and especially to Professor J. B. Farmer for 
his constant supervision during its progress. 
EXPLANATION OF PLATE 5. 
[a & a, —eolumnar cells; 6=strand of elongated cells; c—cork cambium ; 
d=the dise ; e—epidermis; /—foliage-leaf scar; s= vascular ring of stem.] 
Fig. 1. Portion of stem with leaves removed, showing discs (about natural 
size), 
Fig. 2, Transverse section of part of stem, illustrating development of dise. 
a & @,. Columnar cells, which give rise to hairs. . 
b. Elongated cells, eventually forming the vascular connexion with 
the xylem of the stele, 
