IN VEGETABLE BIOLOGY. 853 
obliquity being on the right side of the left and on the left side 
of the right leaf; but they are much like them in structure, the 
chief differences being that the stomata are upon the upper 
instead of on the under face, and that the epidermal cells in the 
oblique portion are isodiametral as elsewhere. 
A section of a large leaf in a plane perpendicular to its own 
shows the cup-shaped epidermal cells of the upperside, which, 
having their long axis at right angles to the plane of the leaf, 
bear some resemblance to palisade-cells ; they touch at their sides, 
but taper off somewhat so as to leave narrow interspaces between 
their inner ends (Pl. XIII. figs. 1 a-c). Lying upon the whole of 
the inner and a part of the lateral walls is the saddle-shaped 
ehlorphyll body ; thus, when looked at from above, the leaf of 4 
healthy plant growing in diffused light presents to view a number 
of bright green disks separated from each other by the cell-walls. 
This is, however, true only of the upper three-fourths of a leaf ; 
at its base and throughout the oblique portion the chlorophyll 
body is either horseshoe-shaped (fig. 2) or, as usually happens, it 
has undergone division, or at least shows signs of division, into a 
variable number of irregularly-outlined cleavage-masses, which 
may be quite separate from each other or remain in connection 
by means of a fine strand of colourless plasma (figs. 3 a-d). 
Division may be so complete in many of the proximal and oblique- 
portion cells and the cleavage-masses may round themselves off 
80 perfectly that the chlorophyll then takes on very much the 
appearance of ordinary grains (fig. 4). Underlying the midrib 
are three layers of stellate mesophyll-cells with granular chloro- 
phyll; this tissue thins out towards the leaf's edge and disappears 
at some little distance therefrom. The chlorophyll of the lower 
epidermal cells resembles that of the elongated cells of the upper 
layer. There is great diversity in the form assumed by the 
cleavage-masses, especially towards the leafs apex—a very 
common condition being that of a straight or curved chain with 
fine connecting threads between the round chloroplasts (figs. 5 
& 6 a-d). The chlorophyll of the small leaves is very similar, but 
inasmuch as the upper epidermal cells are all isodiametral or 
nearly so, the saddle-shaped chloroplasts are found everywhere 
except at the very base *. . 
If strong sunlight be allowed to stream upon S. Martensii the 
* Also upon the long apiculus with which these leaves are provided, 
2r2 
