94 



GROWTH AND WORK OF PLANTS 



leaf, so that the water is conserved. These leaves often closely 

 overlap or lie close against the stem as scales. The cassiope 

 (Cassiope tetragona) , which is found in sphagnum moors in some 

 of the Northern States, and is common from Labrador to Green- 

 land and Alaska, is an example. 



151. Needle-like leaves. These are found on many coni- 

 fers, especially the pines. The leaves are long, narrow, and 

 thick, and are called needle leaves. They have a thick, waxy 

 cuticle, an epidermis with thick walls. Beneath the epidermis 

 there are several layers of cells the walls of which are very thick 

 and hard, and inside is the mesophyll. This form and structure 

 of the pine leaves enables them to conserve water so that they 

 lose it very slowly; otherwise the leaves would lose so much 

 water that in winter the trees would be killed. The spruces have 

 similar leaves, but they are shorter and more flattened, while some 

 other evergreens have scale leaves, which with their structure 

 enable them to endure the drying effect of the cold winters. 



Fig. 79. 

 Tendrils of sweet pea coiling around supports. 



152. Modifications of leaves combining the normal func- 

 tions with other utilities. First, tendrils and tendrils on 

 leaves, as in the pea; also where the petiole of the leaf functions 

 as a tendril, as in the virgin's bower (Clematis). Second, the 



