PLANTS OF THE SOTOL REGION 627 
The rather deep grooves (f. 5, Sg) widen out at the bottom, 
thus making a still-air chamber which is cut off from too free com- 
munication with the outside by the development of very numerous 
overlapping finger-like processes (/, f) equivalent to the hairy 
investment of stomatal pits in some plants. From the bottom and 
deeper sides of the groove, the stomatal pits proper (sf) descend 
through a thick epidermal wall to two very simply arranged and 
apparently rather immobile guard-cells ( g) beneath which is an 
intercellular chamber (7) leading by various small channels to 
adjacent assimilation cells (as). 
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Fic. 6. Transverse section of leaf of Molina Texana. m, m, girders of bast- 
like mechanical tissue enclosing the vascular conducting strands, vs, and alternat- 
ing with bands of assimilation tissue, as; ce, sheath of non-chlorophyl-bearing (trans- 
portation ?) cells investing the bast areas ; other parts as above. >< = 25. 
The assimilation tissue is, as one would expect, arranged with 
reference to the grooves, showing in cross-section a somewhat V- 
shaped zone of cells arranged along the sides of the groove and 
reaching from its bottom interior-ward to the apex of the V, grad- 
ually becoming isodiametric, thicker walled, storage-cells with 
much pitted walls. 
3. Nolina Texana.—In the case of Nolina, the leaves are 
long, linear and grass-like, though rigid. They possess almost 
NO storage tissue in the interior and the mechanical ribs extend 
across the leaf as girders (f. 6, m, m) separating the assimilation 
areas (as), which also reach across the thin diameter. Thus the 
