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Transactions. 



The spongy tissue is composed of about 6 rows of cells. In the upper 

 part of the leaf these cells are about the same length as breadth, but 

 just above the lower epidermis they are narrower and are elongated in a 

 direction parallel with the surface of the leaf. These cells also have thin 

 walls and contain oil, -which is more abundant nearer the upper than near 

 the lower surface of the leaf. 



The lower epidermis consists of cells which are oval in transverse 

 section. Many of them are produced into long, stout, several-celled hairs 

 which have thin walls. The lowest ceU has a thin cuticle. These hairs 



Fig. 17. — Celmisia longifolia var. gracilenta. Transverse section of 

 sheathing leaf-base ( X 175). a, upper epidermis ; 6, hyj^o- 

 derma ; c, mesophyll ; d, stereome ; e, xylem ; /, phloem ; 

 g, multicellular hair. 



are much longer and thicker than those of the upper surface (and those 

 beneath the midrib), and they do not form such a dense mass, so that 

 their form can be seen more easily. 



Stomata are confined to the lower surface of the leaf, where they are 

 numerous. As is often the case with leaves which have a dense tomentum, 

 the stomata are raised above the epidermal cells. The guard-cells have 

 very thick walls, and there are guard-cell ridges. 



Sheathing Leaf-hase (figs. 16 and 17). — Fig. 16 gives a schematic view of 

 this ; fig. 17 shows the structure in detail. 



