342 



FORM AND POSITION OF THE TRANSPIRING LEAVES AND BRANCHES. 



narrow secondary grooves leading from it, as can be seen in a vertical section of 

 an open leaf of Festuca alpestris, a plant very almndant in the Southern Alps (see 

 fig. 86°). In Festuca alpestris, the lilunt apex of each ridge has a border, three 

 layers deep, of cells destitute of chlorophyll, and the lower side of the leaf is pro- 

 vided with an actual armour of thick-wuUed bast cells, covered by an epidermis. 



Fig. 86— Folding of Grass-leaves. 



1 Vertical section through part of the open leaf of Slipa capillata; x240. - Vertical section tlinmgh an entire open leaf. 

 3 Vertical section through a closed leaf; x30. «Vertical section through a portion of the leaf of Festuca alpestris; x21Ü. 

 ' Vertical section through an entire open leaf. <• Vertical section through a closed leaf; x30. 



whose outer walls are much thickened. A vertical section through the leaf of 

 Festuca punctoria, a native of the Taurus, is represented in fig. 88. In this 

 plant, the leaves, when open, present a fairly shallow depression; the under surface 

 is clothed with a protective mantle of five layers of strong cells devoid of chloro- 

 phyll; the ridges are rounded off and possess only a single layer of covering cells, 

 provided with an extremely strong wax-like coat. The open leaves of Festuca Porcii, 



