THE 
AMERICAN NATURALIST. 
VoL. xv. — OCTOBER, 1881.— No. 10. 
ON THE DEVELOPMENT OF THE STOMATA OF 
TRADESCANTIA AND INDIAN CORN. 
BY DOUGLASS H. CAMPBELL, 
a we examine a portion of the epidermis from the lower sur- 
- face of the leaf of the common trailing Tradescantia ( 7. vu- 
Sais ), it will be seen to consist of polygonal cells, mostly irregu- 
lar hexagons. At intervals, sometimes in nearly straight rows, in 
other cases irregularly, are found the stomata, each consisting of 
two semilunar guard-cells, meeting at the ends so as to enclose a 
central pore, whose walls are thicker than the external walls of 
the guard-cells. These guard-cells contain chlorophyll in distinct 
grains, while in the cells of the epidermis it is wanting. Grouped 
around the stoma are four cells, one on each side, one above and 
one below. These are very different from the ordinary epidermal 
cells, being nearly oblong in shape instead of hexagonal. On 
the stems the epidermal cells are elongated, and although acces- 
sory cells are still present, they are much longer and narrower 
(Fig. xrx). If a vertical section is made through the stoma, the 
guard-cells as well as the accessory cells are seen to be much shal- 
lower than the ordinary epidermal cells, so that a large air-cavity, 
€qual to nearly the area of these four cells is formed beneath the 
stoma, and communicates with the external air by means of its 
pore, If we examine as young a leaf as can be had, the epider- 
mis will be found to consist of nearly regular hexagonal cells. 
When a stoma is to be formed, a septum is formed across one 
end of a cell, at right angles to the axis of the leaf, thus pro- 
_ * Special course of in estigation of plant structure and physiology, conducted in 
the botanical laboratory of the University of Michigan. : : 
a VOL. XV.—No. x. —— 
