366 MR. H. M. CHIBBER ON THE MORPHOLOGY 
cells of the epidermal layer are isodiametrie in surface-view, the diameter 
measuring about 45 w*; in height they average only 15 д. Their lateral 
walls are quite straight. Stomata are absent from this surface ; but the 
epidermis is diversified by the basal cells of hairs and by peculiar aggre- 
gations of small cells, the significance of which is rather obscure. 
Regarding the hypodermal cells they are not only larger іп surface-view, 
as mentioned above, but also in height (Pl. 18. fig. 22). In a slightly wilted 
condition their lateral walls show bellows-like foldings. This indicates a 
provision for reducing the size of the lumina of the cells of this aqueous 
tissue when necessary. When fully expanded, the height of the cells of the 
hypoderma measures about 45 y, i. e. three times that of the epidermal cells. 
The hypoderma is diversified by the presence of secretory cells (РІ. 19. 
fig. 35). These are spherical in outline, measure about 27 ш across, and 
contain among other things an essential oil. One of their peculiarities lies 
in acquiring full dimensions from almost the beginning. Thus in a leaf 
measuring 2:5 em, in length the hypodermal cells appeared cubical and only 
9 u across, i. e. one-fifth their full size; while the secretory cells measured 
full 27 p across, i. e. their maximum size. Occasionally hypodermal cells 
show peculiar thickenings of the walls (РІ. 18. fig. 20). They often look like 
tubercular swellings. Several may arise at a junction of cells and meet 
together by their bases. They are best seen in surface-sections. Their 
significance is obscure. They are probably silicitied. They recail the peg- 
like processes to be seen in the epidermal cells adjoining the guard-cells on 
the walls common to both in Penwa myrtoides and Sarcocolla fucata of the 
natural order Penæaceæ t. The hypodermal layers are close-packed, no 
intercellular spaces being present. 
Outer Wall of Epidermis.—The outer wall is well developed on the upper 
surface. It measures about 4 p in thickness. It is homogeneous and free 
from all tuberosities or striations; hence the upper surface looks polished 
and glossy. 
Hairs.—The hairs are of one type only. Omitting the stalk-cell, they 
would be unicellular. They number about 1200 to a square centimetre. 
They are inserted in very shallow depressions. The  stalk-ceil is very 
peculiar (Pl. 18. fig. 17) ; its cavity is hourglass-shaped, with the difference 
that the lower or inner bulb is larger than the upper or outer bulb. The 
larger bulb is sometimes flattened out (fig. 19). The walls are very 
peculiarly thickened. Тһе base and apex are left unthickened. The 
maximum thickening is in the region of constriction, The cell thence 
broadens both upwards and downwards. Upwards it broadens into an 
* All microscopic measurements have been taken with the ocular and stage micrometers, 
and drawings have been made with an Abbe Camera lucida. 
T Solereder’s ‘Systematic Anatomy of Dicotyledons, Engl. Trans. p. 722. 
