1142 Summers.—On the Occurrence of Lens-cells in the 
cases there is a tendency for the lens function to be shut out by an encrusta¬ 
tion, but this is the case to a greater extent with the cells of the upper 
epidermis. A blurred image, therefore, results. 
The two inner and younger leaves also are provided with the encrusta¬ 
tion, but not to such a large extent as is the case with the older ones. Con¬ 
sequently, before removal of the calcium oxalate, the lens function is more 
efficient than in the cells of the upper epidermis of the older leaves. 
In studying the plants raised from seed an examination was first made 
of seedlings aged three and ten days respectively. In none of these were 
lens-cells developed, there being no sign of papilla-like structures. The 
Fig. 8 . Cells from upper epidermis of a seedling 20 days old. 
cells of the upper epidermis were wavy in outline, as in ordinary epidermal 
cells from the under side of a bifacial leaf; the stomata were not sunken, 
and there was no encrustation. The whole of the ground-tissue elements 
were chlorophyll-containing (Fig. 8). 
When the ‘ Linsenversuch 1 was carried out with strips of the epidermis 
of such seedlings it was impossible to obtain images through their cells. 
The first traces of an encrustation were detected in the upper epidermis 
of plants forty days old. It had not as yet developed in the side epidermis, 
while those of the upper surface still retained their wavy outline and 
exhibited no sign of a papilla-like structure. 
Seedlings sixty-five days old showed a greater increase in the intensity 
