THE WHITE LILY 163 



the leaf, forming what is called arm-palisade tissue. 

 The effect of the branching is that extra vertical 

 wall-surface is gained for the disposal of chlorophyll 

 granules. We must not suppose that this kind of 

 tissue is peculiar to Monocotyledons. 



The lower part of the tissue of the leaf is spongy ; 

 its cells are branched irregularly in all directions 

 (see Fig. 63, s.p.), so as to leave large intercellular 

 spaces between them. 



The epidermis consists on both surfaces of the leaf 

 of large elongated cells, with a thick outer wall, 

 limited by a well-marked cuticle. The stomata are 

 mostly on the lower surface, though we may find a 

 few scattered about in the upper epidermis as well. 

 Each stoma consists of two guard-cells, with a pore 

 between them, leading to an air-chamber below. In 

 fact, their structure is precisely the same as in the 

 Wallflower, but in the Lily they are much larger and 

 easier to observe. 



The bulb-scales also are leaves or bases of leaves, 

 as we have seen. They have, however, quite different 

 functions to perform from the foliage-leaves, and 

 accordingly have quite a different structure. They 

 are not exposed to light, and therefore have no 

 chlorophyll. The epidermis is without stomata. The 

 ground-tissue is very abundant, and is all alike, there 

 being no need for any special palisade or spongy 

 tissue. The cells are crammed with reserved food- 

 material, especially starch, which is gradually con- 

 sumed as the flowering stem develops. The vascular 

 bundles are much fewer than in the foliage-leaf, and 



