Curvature of Tendrils. 395 
would be communicated directly to the ectoplasmic layer on 
the opposite (inner) side of the wall of the cells touched, 
which under ordinary circumstances would be several in 
number. The failure of the impact of liquids at ordinary 
temperatures to produce a reaction, is probably due both to 
the smallness of shock and the fact that it is received over the 
entire outer surface of the wall. Pfeffer has noted an ex- 
tension of the ectoplasmic layer into the outer wall of the 
epidermal cells of the irritable surface of tendrils of Cucumis 
sativa (XVIII, p. 525), a structure absent from any other 
material examined by him or myself. The epidermal layer 
is broken in places by stomata, which communicate with the 
cortical parenchyma by very narrow intercellular passages. 
The collenchyma-layer is one, two, or three cells in thickness. 
The tangential walls are much heavier, and show a number of 
perforations. No great difference in these respects can be 
made out between the concave and convex sides. The 
protoplasm of the concave side almost completely fills the 
cells, and is very densely granular, in marked distinction to 
that of the convex side. Moreover the contents of the 
collenchyma-cells of the concave side, when treated with 
a mixture of eosin-haematoxylin, take on a yellowish violet 
tinge, due to the absorption of the eosin by the innumerable 
minute granules which it contains. The marked difference 
between the contents of the collenchymatous tissue of the two 
sides, favours the presumption that the densely granular con- 
dition of those of the concave side bears some connexion with 
the transmission of impulses transversely or longitudinally ; 
although it is not to be forgotten that the granular contents 
are used during the thickening of the cell-walls, after con- 
tinued curvature, and their presence might be solely as reserve 
substance. The parenchymatous tissue internal to the collen- 
chyma exhibits marked differences in form and behaviour. 
The parenchyma cells of the concave side are longer in 
proportion to their width than those of the concave side, and 
their absolute length is no greater than those of the convex 
side (IX, PI. XIV, Figs. 2, 3), while their diameter is less. 
