128 
THE PLANT WORLD. 
rows of cells ( B, C), whose boundaries may be faintly seen in the 
stomal papilla in preparations mounted for some time in glycerine. 
These vertical rows appear to.be continuous down to the proper 
stomal apparatus at the bottom of the chimney. They become 
much more distinct as they pass inward. 
The stomal apparatus at the lower end of the chimney con¬ 
sists of from forty to sixty or more cells which extend down into 
the mass of palisade tissue some distance, thus prolonging the 
chimney. A cross section of this stomal apparatus shows it to 
be almost perfectly circular, or slightly elliptical, and to consist of 
from ten to twelve rows of thinner-walled cells than those which 
form the main portion of the chimney above. At the bottom of 
this structure is the proper stoma ( B ). It closely resembles the 
stomata of ordinary plants. The guard-cells are thick and large, 
and in cross-section are nearly circular. Each is provided with a 
projecting ridge on its upper surface, and these by approximating 
form a small “ front cavity,” the “ back cavity ” being entirely 
absent. 
Beneath the stoma is the usual air-cavity (sc) which is lined 
with irregular and loosely bordered palisade cells. The intercel¬ 
lular spaces in the mass of palisade tissue are very small. 
We have in this extraordinary structure a most effective device 
for protecting the plant against loss of water, while at the same 
time permitting free access of gases. The highly translucent 
epidermis admits light while its high degree of cuticularization 
prevents loss of water. It would be difficult to imagine a struc¬ 
ture with a more perfect adaptation to existence under conditions 
extremely trying to most forms of vegetation.” M. E. H. L. 
THE TEACHERS DEPARTMENT. 
Edited by Professor C. Stuart Gager. 
Moulds as the Cause of Disease. —The fact that bacteria are 
the causes of many diseases is generally known to the public; the 
classification of bacteria as plants and not as animals is less widely 
recognized, and the association of other and more highly organ- 
