294 T 1 . W. Woodhead and M. M. Brierley. 
Text-fig. 36, A, shows a portion of the epidermis of the concave 
side of the coil seen in surface view. To the left of the figure the 
cells are elongated and this form of cell is continued over the 
convex surface. To the right are seen the cells typical of the 
concave side and it will be noted that they have undergone further 
division by vertical walls, which, as shown by Sachs 1 and others, are 
easily distinguished from the original walls. 
B 
A C 
Text-fig. 36. A. Surface view of epidermis on concave side of coil 
showing secondary walls in the epidermal cells. B. L.S. epidermis and 
cortex of concave side, showing secondary division of the cells by both vertical 
and horizontal walls. C. Ditto with a pit in outer wall of epidermis. 
Text-fig. 36, B, shows part of a longitudinal section, in which it 
will be seen that frequently further division has taken place in these 
epidermal cells parallel to the surface ; this secondary division also 
occurs to some extent in the adjacent cortical tissues. In one 
instance a modified epidermal cell was noticed, in which a thin 
triangular pit occurred, as seen in Fig. 36, C, resembling the 
tactile pits, described by Haberlandt. 2 
The guard cells of the stomata on the concave side are level 
with, or slightly below the surface, and the air chambers are small, 
due perhaps to some extent to compression ; while the guard cells 
of the stomata on the convex side are raised above tbe surface and 
the air chamber is larger. Modifications such as these occur only 
on the concave side. 
As the season advances the differences between concave and 
convex sides become more strongly marked. Text-fig. 37, A, shows 
a portion of the outer tissues of an older coil on the concave side; 
here the epidermal cells are more strongly thickened, depressions 
are formed between the cells, and the cell-walls are often wrinkled 
1 J. von Sachs. Lectures on the Physiology of Plants, Engl. 
Transl., 1887, p. 95. 
3 G. Haberlandt. “ Sinnesorgane im Pflanzenreich,” 1901, p. 126. 
