McLEAN: STOMATA OF TWO SPECIES OF CITRUS 103 
both similar to the Achellea type described by Copeland.* They 
differ from this type in having no thickening of the inner half of 
the ventral wall, and in having no ridge of exit. The general 
appearance of the stomata of each sort is shown by drawings 
made under camera lucida (Fic. 1). The stomata were all closed, 
on account of the treatment with alcohol, except for a few rigid 
stomata which remained open. The drawings are of closed 
stomata and therefore represent the minimum widths of aperture. 
Fic. I 
A, B and C. Stomata of Szinkum mandarin, X 570: A, surface view; B, 
median cross section; C, under view. Showing ridge of entrance (r); outer chamber 
(0); pore (~); and dorsal wall of guard cells 
D, E and F. Stomata of Florida seedling grapefruit, X 570, showing same 
parts asin A, Band C. 
The surface views (Fics. 1, A, and 1, D) show the ridge of 
entrance, 7, to be extremely narrow in the Szinkum mandarin, and 
to be broadly oval in the Florida seedling grapefruit. This differ- 
ence was found to be constant and very striking in all of the 
material examined. The average dimensions of the opening in the 
cuticle surrounded by the ridge of entrance in the Szinkum 
* The mechanism of stomata. Ann. Bot. 16: 342, f. 15-17. 1902. 
