20 HYPODERMAL FIBROUS TISSUE. 



primaries are the most comjilete and have all the elements ; the 

 .secondaries have no annular vessels in the laenna, and have the 

 other elements much less pronounced ; the tcrfiaries lack the lat- 

 eral vessels, and are reduced to a slender cord of small dotted 

 vessels and latticed cells, or only the hitticed cells. 



Xot unfrequently there are very small transverse handles run- 

 ning obliquely from one bundle to another. To see thom entire, 

 a longitudinal secuon must be made parallel to the epidermis. 



Hypodermal Fibrous Tissue. — Usually this tissue is found 

 in isolated groups just beneath the epidermis, and consifts of 

 very long,thick-walled cells, Avith overlapping, tapering extremi- 

 ties. There are no intercellular sjiaces. Sometimes these fibers 

 are found at the margins of the loaf only ; often opjjosite the 

 fibro-vascular bundles and in contact with them on the lower 

 side, but separated from them on the upper side by jnirenchyma. 



They protect and strengthen the blade. In some cases they 

 come together and make a continuous band on the lower side of 

 tlie leaf, but never on the upper side. 



In each triangular portion of a leaf of Deschampsia ccespitosa 

 we find three fibro-viuscnlar bundles, a large median one, and two 

 small lateral bundles. Below each is a group of hypodermal 

 fil)ers. 



In Stipa tenacissinia there are five fibro- 

 vascular bundles in one nerve. 



As examples of hypodermal fibers, we 

 have : 



1^. A mere trace in the median line of 



Fig. 41.— a transverse sec- , i i 



tion of about one-seventh of a tiie buulc ; 

 blade of a leaf of Dcitchampsia 



ciVSDitosa, showini,' one lartje oc \ jrroup at the keel of tlie blade 

 and two small flliro-vascular » t 



bundles, with hypodermal -, a i, ^ ...,,;„ , 



ftbers below each bundle. I* and oiie at cacli margin; 



50.— (Sudworth.) 



3°. Groups, as in the hotter case, with others in certain places 

 on the lower side, or with a continuous layer on the lower side ; 



