60 MEMORANDA. 
stems and petioles of the Nymphzacez, occur also as a 
noticeable feature in the leaves, as 1s well seen in a vertical 
section of the floating leaf of the common yellow water-lily. 
They are readily distinguished from the cells forming the 
parenchyma of the leaf, by their large size and tuberculated 
walls, as well as by the absence of chlorophyll in their 
interior. They lie in the compact upper layer of parenchyma, 
but as their finger-like processes pass mostly upwards and 
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Perpendicular section 
Perpendicular section of upper layer of leaf through the leaf of Nuphar. 
of Nuphar. Mag. 300 diam. Mag. 300 diam. 
downwards, the latter project more or less into the air-spaces 
among the cells of the spongy tissue on the lower side of the 
leaf, while the superior processes reach quite to the upper 
epidermis, where, in these floating leaves, the stomata are 
situated, the lower surface, like that of submerged parts 
generally, having none. It is difficult to make out the rela- 
tion of the cell-processes to the stomata, as the latter are small 
and very indistinct in a vertical section, but, im some cases, at 
least, these pores seem to open just over the terminal points 
of the processes. In such cases, the stellate cells may serve 
the purpose of establishing an indirect communication be- 
