36 HYPODERMAL FIBROUS TISSUE. 



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

 secondaries have no annular vessels in the lacuna, and have the 

 other elements much less jjronounced ; the tertiaries lack the lat- 

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

 vessels and latticed cells, or only the latticed cells. 



Not unfrequently there are very small transverse bundles run- 

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

 a longitudinal section must be made parallel to the epidermis. 



Hypodermal Fibrous Tissue. — Usually this tissue is found 

 in isolated groups just beneath the epidermis, and consists of 

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

 ties. There are no intercelliilar spaces. Sometimes these fibers 

 are found at the margins of the leaf only ; often opposite the 

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

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



They protect and strengthen the blade. In some cases they 

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

 the leaf, but never on the upper side. 



In each triangular jDortion of a leaf of Descliampsia ccespitosa 

 we find three fibro-vascular bundles, a large median one, and tAvo 

 small lateral bundles. Below each is a group of hypodermal 

 fibers. 



In Stipa tenacissima there are five fibro- 

 vascular bundles in one nerve. 



As examples of hypodermal fibers, we 

 have: 



l*^. A mere trace in the median line of 



Fig. 41.— a transverse sec- inn 



tion of about one-seventh of a the blade ', 

 blade of a leaf of Dei<champsia 



ccespitosa, showing one large o^'. A ffroup at the keel of the blade 



and two small nbro-vascular o i 



bundles, with hypodermal ■. , i ^„ „„„;,, . 



fibers below each bundle, ix and one at each margm; 



50.— (Sudworth.) 



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

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



