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BOTANY 



thickened epidermal walls. Frequently the epidermal cells adjoining the guard- 

 cells are less thickened or lower than the other cells of the epidermis (Fig. 104). 

 Such special epidermal cells are called subsidiary cells. 



The stomata are formed by the division of a young epidermal cell into two cells 



Fig. 104.— Epidermis from the under side of a leaf of Tradescantia virginicu. A, In surface view ; 

 B, in transverse section ; I, colourless rudiments of chromatophores surrounding the nucleus. 

 (X 240.) 



of unequal size, one of which, the smaller and more abundantly supplied with 

 protoplasm, becomes the stoma mother -cell; while the larger, containing less 

 protoplasm, usually continues as an epidermal cell. The stoma mother - cell 



Fig. 105. — Transverse section of the epidermis of Aloe nigricans, 

 i, Inner, uncutinised thickening layer, (x 240.) 



becomes elliptical in outline and divides again, by a vertical wall, into the two 

 guard-cells, between which, by a splitting of the wall, the intercellular passage 

 is formed. Before the formation of the definitive stoma mother-cell, successive 

 divisions of the young epidermal cell often occur ; in such cases the finally 

 developed stoma is generally surrounded by subsidiary cells. 



Stomata are chiefly developed on the green parts of plants, but are 

 sometimes found even on the coloured floral leaves. They are natur- 

 ally found in greatest numbers on the leaves, as it is there that they are 



