THE EPIDERMAL SYSTEM. 



103 



(rf) In the plants he examined he found that there were 

 B4 species with from 1 to 100 stomata per bc[. mm. = 645 to 64,600 per Bq. inch 



(e) Morren's measurements* vary somewhat from those given by 

 Weiss. The following, not given by Weiss, are taken from Morren's 

 ■table : 



(/) Tlie stomata of the so-called Compass Plant {Silphium lacinia- 

 ium) are nearly equal in number on the two sides of tlie vertical leaves ; 

 there are on the true upper surface 83 per sq. mm. (= 53,700 per sq. 

 inch), and on the under surface, 87 per sq. mm. (= 57,300 per sq. 

 ■inch).f 



(g) On most leaves the stomata are not distributed equally over all 

 -portions of either surface ; they are not found on the veins^ but are 

 restricted to the areas between them. In some plants this restriction 

 is accompanied by a further modification, as in Oeanothus prostratus, 

 where the stomata are confined to tlie bottoms of sunken pits which 

 occur on the under side of the leaves. In the long harsh leaves of 

 Stipa apa/rtea the stomata of the upper surface are restricted to the 

 sides of the deep longitudinal channels which lie between the promi- 

 nent nerves. (See Figs. 135-6, page 158.) 



* Published first in Bulletin de VAcademie royale de Belgique, vol. 

 16, number 12, 1864, and also in part in Pringsheim's " Jahrblicher," 

 etc., 1. c. 



f See an article in American Naturalist, 1877, p. 486 : " Observations 

 ■on SlilpMum laciniatum, the so-called Compass Plant," by C. E. Bessey. 



