LOSS OF WATER 



31 



in many forms and disguises, and readily adjusting itself 

 to wide variations in its surroundings. By virtue of this 

 characteristic, it helps to enable the plant as a whole to 

 become adapted to its surroundings. For the present 

 purpose, we are primarily interested in leaves as foliage. 



33. Internal Anatomy of the Leaf-blade. — If we take 

 any convenient foliage-leaf, such as, for example, a leaf 



Fig. 23. — ^Leaf of a live-for- 

 ever (Sedum Sp.), with a por- 

 tion of the epidermis peeled 

 back. Underneath the epi- 

 dermis is the mesophyll. 



Fig. 24. — Mullein (Verbascum Thap- 

 sus). L, cross-section of leaf- blade, 

 showing relative thickness of layer of 

 epidermal hairs; H, a single hair from a 

 leaf (greatly magnified). 



of the common lilac, we may readily demonstrate, with 

 the aid of a scalpel or sharp knife, that the surfaces of 

 the blade are covered with a thin skin or epidermis, 

 which may be peeled off (Fig. 23), disclosing the mid-leaf 

 substance (mesophyll), lying between the upper and the 

 lower epidermis. In many leaves (for example, those of 



