84 VI. THE EPIDERMIS STOMATA. 



tioned, which appears coloured yellow-brown by the chlorzinc 

 iodine, because it is cuticularised. As an extremely delicate 

 membrane, the cuticle is continued through the stomatic cleft, 

 over the guard-cells, to the commencement of the chlorophyll- 

 containing parenchyma. Apart from this, the guard-cells are also 

 violet over their whole wall. By the use of concentrated sul- 

 phuric acid the whole section is dissolved, the cuticle alone 

 remaining behind, together with the cuticularised projections of 

 the guard-cells. 



Stomata of Hyacinth. The stomata on the leaves of various 

 species of Hyacinth are constructed exactly as in Iris, though 

 not sunk in the epidermis (i.e., there is no stomatic pit), the 

 two guard-cells lying at approximately the same level with the 

 surrounding epidermal cells. Surf ace- sections, therefore, or 

 epidermal strips torn off, show the two guard-cells when viewed 

 right way up. The stomata are found not only on the under, but 

 also on the upper, side of the leaf. As the long axis of the stoma 

 in this case also coincides with the long axis of the leaf, it is easy 

 to obtain cross-sections. At half-way up on the side towards 

 the cleft, as well as on the whole side facing the surrounding 

 epidermal cells, the wall of the guard-cells is slightly thickened. 

 The structure of the " hinge " is the same as in Iris. 



Stomata of Tradescantia. An exceedingly favourable object 

 for the study of the stomatic apparatus is found in the hardy 

 spider-wort, Tradescantia virginica. The epidermis on both 

 sides of the leaf consists of polygonal cells, mostly elongated in 

 the direction of the long axis of the leaf ; with these alternate 

 narrow stripes of longer and narrower cells. These stripes are 

 visible with the naked eye, especially on the under surface of the 

 leaf, and appear green in colour, while the stripes of broader cells 

 appear grey. The lateral walls of the epidermal cells are pitted ; 

 the outer surface is faintly striate. The number of stomata is 

 markedly greater on the under side of the leaf ; therefore we 

 choose this side for examination. The stomata are almost 

 always surrounded by four epidermal cells (Fig. 30, A). The 

 guard-cells lie on the same level with the epidermal cells ; the 

 cleft which they have between them is comparatively large ; they 

 contain chlorophyll grains, between which the nucleus is usually 

 visible. In the epidermal cells also the nuclei are very con- 

 spicuous, and appear surrounded by small colourless leucoplasts 

 (Fig. 30, A, I) ; the cell-sap of the epidermal cells is here and 



