174 PHARMACEUTICAL BOTANY 



The epidermal cells which abut on the stomatal apparatus are 

 called neighboring cells or subsidiary cells. These in many cases, as 

 in species of Helleborus, Sambuscus, Hyacinthus, Paonia, Ferns, etc., 

 are very similar to the other epidermal cells, but in a large number of 

 plants they differ in size, arrangement and shape from the other 

 cells of the epidermis which do not abut upon the stomatal apparatus. 

 In Senna they are two in number one larger than the other and 

 arranged parallel to the guard cells of the stoma; in Coca a similar 

 arrangement occurs but the cells are more even in size, nevertheless 

 they lack the characteristic papillae found on the other epidermal 

 cells; in Pilocarpm they are usually four in number but quite narrow 

 and more or less crescent-si aped; in Uva Ursi their number is usu- 

 ally seven to eight and their arrangement radial around the stomata 

 apparatus. 



On all dorsoventral leaves, the stomata arise more abundantly on 

 the lower epidermis, less abundantly on the upper. Exceptions to 

 this rule are due to the peculiar readaptation of the leaf to its sur- 

 roundings. Thus, in the reversed types of leaves (twisted in a half 

 circle) the stomata, formerly on the lower surface, have migrated to 

 the upper surface which now has become the physiological lower 

 surface. 



In Umbrophytic (shade) plants the stomata are either wholly on 

 the lower surface or partly so with a number on the upper surface. 

 Where the plants are Mesophytic and exposed to dense sunlight and 

 leaves remain dorsoventral, the stomata are on the lower surface; 

 these stomata are large, if the surroundings are damp. If such 

 plants live in dry soil and dry air, the stomata are of small size and 

 numerous; if they dwell in dry soil in hot surroundings and dense 

 light they are very small and frequently sunk. If the plants are 

 Xerophytic and the leaves dorsoventral, the stomata are quite abun- 

 dant, small, with narrow slit, and depressed below the level of the 

 epidermis. 



There are five types of stomatal development, viz.: 



First Type. Each primitive epidermal cell (or the majority, or 

 only certain ones of the epidermis) at the close of the dermatogen 

 stage, gradually lengthens and then cuts off a smaller from a larger 

 cell. The smaller one is equilateral, has a very large nucleus, and is 

 termed the Stoma Mother-cell; the larger, quadrangular, and called 



