526 Bessey: STOMATA OF HOLACANTHA 
boundaries may be faintly seen in the stomal papilla in prepara- 
tions 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 about 40 4, prolonging the chimney 
about 8. 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 (s/). 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 
forma small ‘front cavity,” the Vorhof of the German histologists. 
The “‘ back cavity” or Hinterhof is entirely wanting. The vertical 
height of the stoma is 27 #, and its diameter measured in cross- 
section of the guard-cells is 35 4. Its diameter measured parallel 
to the opening very slightly exceeds its transverse diameter. 
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 ingenious de- 
vice for protecting the plant against loss of water, while at the same 
time permitting free access of carbon dioxide. The highly trans- 
lucent epidermis permits photosynthesis while its high degree @ 
cuticularization prevents water-loss. It would be difficult to im- 
agine a structure with a more perfect adaptation to existence 
under conditions extremely trying to most forms of vegetation. 
