842 



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 abundant in the Southern Alps (see 

 fig. 86^). In Festuca alpestris, the blunt 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-walled bast cells, covered by an epidermis. 



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\u.. \^uy . 



i\v:r- 



^ 



Fig. 86.— Folding of Grass-leaves. 



1 Vertical section through part of the open leaf of Stipa capillata; x240. 2 Vertical section through an entire open leaf. 

 8 Vertical section through a closed leaf; x30. * Vertical section through a portion of the leaf of Festuca alpestris; x210. 

 5 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, 



