624 Bray: THE. Tissues OF SOME OF THE 
during the strain incident to alternate contraction and expansion. 
The cells of the assimilation zone are more or less palisade in ar- 
rangement and somewhat elongated, becoming interior-ward more 
nearly isodiametric and again thicker walled with numerous pits 
and large intercellular areas. Here, it is no longer assimilation 
but storage tissue. 
The stomata are the specially interesting structures, naturally, 
since to them is entrusted the precarious function of opening a 
channel of communication from the external environment to the 
Agave Lecheguilla. 
Fic. 1. Surface view of stoma, showing the stomatal pit blocked by two projec- 
tions Z, 2, fore-and-aft. 
Fic, 2. View of stoma shown in /, z obtained by focusing on horizon immedi- 
ately below 1. Projections from right and left block the passage by a compressed fun- 
nel-like structure ( /, f) seen in cross-section in f. 4. 
Fic. 3. The guard-cell apparatus lying below horizons 1 and 2. Obtained by re- 
moving thin tangential section of epidermis. g, g, guard-cells; @, a, auxiliary aie 
The orientation and magnification of the stoma is the same in the three figures- 
delicate interior tissues, a fact equally true of each of the other spe- 
cies. The guard-cell apparatus of the stomata appears in surface 
view very much like that of numerous other Liliiflorae, the guard- 
cells proper being partially surrounded and held in place by the 
very much larger auxiliary cells (/. 3) put the protective appa- 
ratus above these is quite peculiar and different from any types with 
which the writer is familiar. Exterior-ward, where the stomatal 
pit opens upon the surface, two prominent projections of the epl- 
dermal walls fore-and-aft almost meet midway and block the pas- 
sage except for two triangular entrances right and left (7. 1). 
Below this, two more complex projections from right and left 
again almost meet midway, leaving the merest slit at right angles 
