HYPODERMAL FIBROUS TISSUE. 



27 



4°. Groups above and below the primary bundles only ; 



5°. Groups above and below each bundle, but not continuous; 



0°, Groups above and below each bundle, and contiguous ; 



7°. Groups covering the mesophyll, except some cells bearing 

 chlorophyll on the sides of the nerves. 



The first three of the above are conduplicate in vernation, and 

 the fourth includes all of the species of Amlropixjoti and Panicum, 

 except P. plicafum. So far as the develojiment of hypodermal 

 fibers are concci'ned, Chamafjro.sfis minima and S'fipa tenacissima 

 are extremes. The former i.s illustrated by figure 18, and figure 

 14 will answer as a substitute for the latter. 



"^ aquatic and in annual grasses these fibers are feebly developed, 

 while those grown in extreme dry, hot countries are remarkable 

 for the development of this tissue. Upland grasses grown in the 

 shade, with an ample supply of 

 moisture, have their woody fibers 

 feebly developed. 



When this tissue is well developed it 

 helps prevent the free evaporation of 

 moisture. The closing of the stomata p,,Svf,;rS"mf wiuf weu'^d^ 



, , t , . , . , veloiied liypodermal tissue. 1x80, 



also lielps to retain the moisture. — (Duvai-Jouve.) 



Fig. 43.— Section of a 

 blade of a leaf of Festucu 

 ovhut var. loBvis, with a 

 Kronp of hypodermal 

 fibers below the mid-vein, 

 and one at each margin of 

 the leaf. I x 30.— (Hackel.) 



Fio. 44.— Section of the 

 blade of Foituca orina, 

 witli hypodermal fibers 

 extending over the lower 

 side. 1x30.— (Huekel.) 



Fio. 45. — Seet ion of a leaf 

 of Fetituca ovliia var. i/it- 

 rliiscula ( hard fescue), 

 with hypodermal fibers 

 extending over tlie lower 

 side. 1x30.— (Hacliel.) 



In the last three the bulliform cells are wanting or only feebly 

 developed, and the blades remain closed or nearly closed oven when 



mature. 



