98 PKACTICAL BOTANY. 



3. Vascular bundles of small size : their number 

 varies from 3 to 5. 



Strip off a piece of epidermis from the leaf of Sedum 

 acre, and mount in water. Note : 



1. The Epidermal cells with sinuous outline, 

 nucleated : with no chlorophyll. 



2. The Stomata with two guard cells surrounding 

 the pore as in the Cherry Laurel. Surrounding these 

 are : 



3. Three Subsidiary cells, which differ in size and 

 shape from the ordinary epidermal cells, and are 

 arranged in definite order round each stoma. 



Beneath the epidermis will usually be found cells of 

 the mesophyll, with thin walls, large vacuole and 

 protoplasmic sac, in which are embedded chlorophyll 

 grains. 



By making similar preparations from successively younger 

 leaves the development of the stoma and subsidiary cells may be 

 traced as follows. From, one of the similar epidermal cells a 

 smaller cell is cut off, from this are successively cut off the three 

 subsidiary cells, the remaining cell is the mother-cell of the 

 stoma, which divides to form the two guard cells. 



On the leaves of many plants, stomata of large size are to be 

 found situated above the free endings of the vascular bundles of 

 the lamina, and especially at the tips of the teeth : these are 

 often incapable of closing, and are concerned in the secretion 

 of water : hence they are called water-stomata. In certain 

 cases (Saxifragacece and Crassulacece) a mass of cells of the 

 mesophyll is specially differentiated as glandular tissue (the 

 water-gland) ; it is connected with the termination of a 

 vascular bundle. 



