HYPODERJUAL FIBROUS TISSUE. 



97 



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



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



G°. 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 A ndropogon and Panicum, 

 except P. plicattwi. So far as the development of hypodermal 

 fibers are concerned, CJiamagrostis minima and Stipa tenacissima 

 are extremes. The former is illustrated by figure 18, and figure 

 14 will answer as a substitute for the latter. 



In 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 evaj)oration of 

 moisture. The closing of the stomata p^,^.;ru;n^t:^l:^n?!^'^'^ln7^ 



, ^ 1 , ■ ±^ • , veloped hypodermal tissue. 1x50. 



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



Fig. 43. — Section of a 

 blade of a leaf of Fvatuca 

 ovina var, Icevis, with a 

 group of hypodermal 

 fibers below the mid-vein, 

 and one at eaeh marg-in of 

 the leaf. 1 x 30.— (Hackel.) 



Fig. 44.— Section of the 

 blade of Festuca ovina, 

 with hypodermal fibers 

 extending over the lower 

 side. 1 X 30.— (Hackel.) 



Fig. 4.5.— Section of a leaf 

 of FeMuca avuia var. du- 

 riiu^cula hard f c s c n e ), 

 with liypodermal fibers 

 extendiii;: over tlie lower 

 side. 1 X 30.— (Hackel.) 



In the last throe the bulliform cells are wantiijg or only feebly 

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

 mature. 



