FORM AND POSITION OF THE TRANSPIRING LEAVES AND BRANCHES. 



341 



walls under the epidermis; the same thing occurs on the under side of the leaf (i.e. 

 at the base of the ridges), which is formed of one or several layers of cells without 

 chlorophyll, but furnished with thickened walls. The closing of the leaf is not so 

 simple here as in the Seslerias. There the leaf-folding only produced a single deep 

 channel, widened at its base; in the fescue-grasses all the small grooves between 

 the ridges become narrowed by the closing, i.e. by the upward inclination of the 

 right and left halves of the leaf, those adjoining the central ridge to the greatest 



Fig. 85.— Folding of Grass-leaves. 



1 Vertical section through an open leaf of the thin-leaved Moor-grass (Sesleria tenuifolia). 3 Vertical section through 

 a closed leaf; x40. » Portion from the centre of an open leaf ; x300. 



extent, those in the neighbourhood of the approximated margins in a lesser degree 

 (see fig. 88^). Since the stomata lie on the sides of the ridges, it is obvious that 

 transpiration is checked to the utmost by the closing and consequent approximation 

 of the opposite sides of each groove. 



In individual cases among various fescue-grasses are to be found manifold 

 differences in the number and shape of the ridges, also with respect to the formation 

 of the under surface of the leaf, and most of all in the form assumed by the leaf in 

 its expanded condition. There is a large group of festucas which are said to be 

 poisonous by the shepherds in the mountain regions of Spain, and in the Alps, the 

 Taurus, and the Elbruz. These will be spoken of again later. When open in 

 damp weather they form only a moderately narrow main furrow, with several 



