FIBRO- VASCULAR BUNDLES. 25 



FIG. 40. Section of a blade of i leaf of Festuca rubra. I x30. (Hackel.) : 



The object accomplished by the closing or rolling of the leaves 

 is to cover one surface and assist in preventing excessive evapora- 

 aatioii in dry weather. 



The bulliform cells in their size, number, .and arrangement 

 may be used for critical specific characters. 



Sedges, Cyperacce, often have one band of very large bulliform 

 cells' in the median line, and uniformly on the iipper side. 



These modes of arrangement of the bulliform cells is especially 

 important in a physiological point of view, as they produce vari- 

 ous motions of the leaves. 



Fiforo-vasciilar Bundles. In all grasses the structure of 

 these is much the same. There are two, rarely four, large pit- 

 ted vessels, placed side by side near the middle of a bundle, at 

 equal distances from the lower epidermis. The reader will here 

 find it profitable to consult figure 5 for tracing out details. 



Between these is a group of small reticulated cells, as many as 

 fifty in Festuca arundinacea, or only two or three in Panicum 

 Crus-galli (barn yard grass) and Leersiaoryzoides (rice cut-grass). 

 Above this group, towards the upper side of the leaf, and in a 

 median line of the bundle is one or more annular or spiral ves- 

 sels, situated near an air cavity, made by a breaking away of the 

 cells. 



On the opposite side, always on a median line, is a group of 

 latticed cells or soft bast. 



Surrounding all of the above is the bundle sheath formed of 

 long, thick walled cells ; and about the whole bundle is the thin- 

 walled parenchyma of the fundamental tissue. 



The bundles are not all developed to the same extent. The 



