626 Bray: THe Tissurs oF SOME OF THE 
between interior and exterior and so fortify the plant against dan- 
gers entailed in such an exchange in so arid a climate. The air- 
chamber beneath the guard apparatus (/ 4, 2) is relatively large 
and has ample connections by many channels with adjacent chloro- 
phyl-bearing cells. 
2. Hesperaloe parviflora. — This Yucca-like plant has relatively 
soft and succulent leaves as compared with the true yuccas, and 
with NVolina, to which it would appear to have some genetic rela- 
tion judging from the identity of stomatal structures. The long 
} Me REO wean 
Fic. 5. Transverse section through superficial part of leaf of Hesperaloe parvi- 
flora. sg, stomatal groove; f, f, the blocking projections ; sf, the stomatal pit ; 7, po 
tion of bast-like mechanical rib; other abbreviations as before. 
and rather slender and flexible leaves are longitudinally grooved 
and ridged, the grooves (/. 5, sg) providing a favorable location 
for the development of stomata, and the intervening ridges being 
ribs of bast-like, mechanical tissue (, ). In the case of Nolina 
(f. 6, m, m) these ribs pass completely across the narrow diameter 
of the leaf, while in Hesperaloe they reach perhaps less than one 
third the distance across. 
