80 



IOWA ACADEMY OF SCIENCES. 



THE STOMATA AND PALISADE CELLS OP LEAVES. 



BY F. C. STEWART. 



The name stomata (sing, stoma) has been applied to the elliptical apertures in 

 the epidermis of leaves and other green parts of plants. The stoma is a modified 

 epidermal cell and consists of a rift and guradian cells (usually two in number). 

 The guardian cells are rightly named for it is their function to regulate the amount 

 of evaporation from the leaf by opening and closing the rift. Unlike ordinary 

 epidermal cells, the guardian cells contain chlorophyll, and for that reason they 

 were once thought to belong to the parenchyma. 



Goodale^ says, " Stomata belong especially to green organs exposed to the air, 

 but they have been detected on all superficial parts of the plant with the exception 

 of roots." As authority he cites De Bary, who found stomata on the tubers of the 

 potato, on the perianth and anthers of Liliittn hidbifertim and on the pistil and 

 seed coat of the Canna. In the higher plants they occur for the most part on the 

 leaves. In the majority of Monocotyledons- they are found on both sides of the 

 leaf, but in Dicotyledons they are seldom found on the upper surface except in 

 leaves which present both sides to the sun. In some Coniferce^ there are more 

 stomata on the upper than on the under surface. They are entirely absent from 

 the leaves of submerged water-plants, and appear only on the upper surface of 

 floating leaves. 



In regard to arrangement, there seems to be no general law except in a few 

 orders, viz: in Equisetacece, Conifene and Gramhiece. Since the object of the 

 stomata is to bring the interior of the leaf into communication with the outside 

 they world, are so placed as to communicate directly with the intercellular passages. 

 Their arrangement, therefore, depends upon the internal structure of the leaf. The 

 rift is a narrow ellipse whose major axis is generally the major axis of the stoma as 

 a whole. {Poriitlacca oleracea is an exception.) Outside of the orders above named, 

 the stomata are found scattered irregularly over the surface of the leaf, and with 

 their axes pointing in every conceivable direction. 



Being together with the lenticels, the aerators of plants, their number and size 

 are thought to bear an important relation to the behavior of plants. In general, 

 the plants of arid regions have few and small stomata, while water plants and 

 plants native to moist climates have numerous and large stomata. This rule has 

 a great many preplexing exceptions, and we are foiced to acknowledge that we 



1 Goodale's Physiological Botany, p. 70. 



2 Thome's Struct, and Phys. Bet., Eng. Translation, Bennett, p. 61. 



3 Gray's Struct. Bot., p. 90. 



