348 



ELEMENTARY BIOLOGY 



new cells ; these die as they are moved toward the surface 

 by the newer cells beneath, becoming a layer of dead scales. 

 The skin protects the animals not only against mechanical 

 injury but also against the loss of water and against the 

 absorption of water, for the skin is practically waterproof, being 



FIG. 163. Mullein in meadow 



These plants are closely covered with fine, branching hairs, giving the leaf a flannelly 



texture. We can well imagine that a cow would not care to eat anything that felt like 



flannel in the mouth, and so we can understand that the hairy growth may actually 



protect the plants against grazing animals. (From photograph by Dr. H. A. Kelly) 



more or less oily (see p. 206). It also protects, to a certain 

 degree, against too rapid changes of temperature. In this 

 function many skins are supplemented by layers of fat on 

 the inside and by hairs or fur on the outside. 



399. Hairs and other outgrowths. On the leaves and stems 

 of plants the cells of the epidermis enlarge at right angles to 

 the surface. This mode of growth results in the formation of 

 hairs (see Figs. 162, 163). 



