THE EPIDERMAL SYSTEM. 



103 



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

 54 species with from 1 to 100 etomata per sq. mm. = 645 to 64,500 per sq. Inch 



38 

 89 

 12 

 9 

 1 

 3 



100 to 200 

 200 to 300 

 300 to 400 

 400 to 500 

 500 to 600 

 600 to 700 



= 64,500 to 129,0; .0 

 = 129,000 to 193,500 

 = 193,500 to 258,000 

 = 258,000 to 322,500 

 = 322,500 to 387,000 

 = 387,000 to 451,500 



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

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

 table: 



(f) The stomata of the so-called Compass Plant (Silphium lacinia- 

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

 there are on the true upper surface 82 per sq. mm. (= 52,700 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 Ceanothus prostratus, 

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

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

 Stipa spartea the stomata of the upper surface are restricted to the 

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

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



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

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

 etc., 1. c. 



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

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



