FORM AND POSITION OF THE TRANSPIRING LEAVES AND BRANCHES. 



343 



a native of the Carpathians, are relatively thin (see figs. 87 4 and 87 5 ). Below the 

 epidermis of the under side is no mantle of bast cells as in the species already 

 described, but only isolated strands of bast; however, the crest of each ridge is 

 furnished with a strand of bast cells; the ridges themselves project very much, and 

 the whole leaf is traversed by six deep narrow grooves. 



In the three fescue-grasses cited here as examples, and in all species of the 

 genus Festuca, forming the main part of the turf of our fields, a vascular bundle 



w^^^jV^te^j^^^jl^l y--- --v: v 



Fig. 87. — Folding of Grass-leaves. 



1 Vertical section through a closed leaf of Lasiagrostis Calamagrostis. - Vertical section through an open leaf; x24. 

 3 Vertical section through a portion of the open leaf; x210. 4 Vertical section through a closed leaf of Festuca Porcii. 

 5 Vertical section through an open leaf; x24. 6 Vertical section through a portion of the open leaf; x210. 



surrounded by green tissue traverses each ridge. In the hinged leaves of many 

 other grasses, the green tissue of each ridge is divided into two portions. The 

 vascular bundle is bordered above and below by strands of thick-walled cells devoid 

 of chlorophyll, and thus arises a strong septum in the green parenchyma, beautifully 

 shown in the transverse section of a leaf of Lasiagrostis Calamagrostis, illustrated 

 in fig. 87. In the leaves of the Feather-grass {Stipa ca^illata) are alternating higher 

 and lower ridges; a vertical section is shown in fig. 86 1 ' 2,3 . In the higher ridges 

 occur septa similar to those in Lasiagrostis, but in the lower there is only a vas- 

 cular bundle surrounded by green tissue as in the fescue-grasses. No less than 



