10 



STRUCTURE < IF THE LEAF 



such leaves as the live-for-ever, blue Sag or hyacinth. The cells 

 of the epidermis arc very compactly put together and may be 

 stripped off by means of a penknife as a thin white skin. Ex- 

 amined under a microscope, such preparations show the stomata 



a> minute openings guarded by two rather lens-shaped cells. 



termed the guard cells (Fig. 6). Chloroplasts usually occur 

 only in the guard cells, the other epidermal cells having a watery. 

 colorless cell content. In addition to these features. Fig. 7 shows 

 that the outer portion of the walls of the epidermal cells is modi- 

 fied so as to form a delicate, skin-like layer over the outer sur- 



Fig. ~. 



In. & 



Fig. ~. Section across a stoma shown in Fig. 6: s, stoma; g, guard cell; 



tide; ii. air chamber, ll. 0. Hanson. 

 Fig. & Hair- tn>m the epidermis of squash leaf. 



of the epidermis. This part of the cell wall is called the 

 cuticle. It contains a substance, cutin, that renders the epidermis 

 nearly impervious to gases and fluids, so that the leaf is entirely 



surrounded by a water- and t, r as -proof coat. In many leaves hairs 



of various form- grow out from the epidermal cells i Fig. 8). 



5. The Mesophyll. The cells within the epidermis have, for 



the most part, a greenish Color due to numerous green hoilies. 



chloroplasts, contained in the cells (Fig. 5, ch). These green 

 cell- of the leaf, termed the mesophyll, consist of one or more 



of rather elongated and compact cells on the upper side 



of the leaf (the palisade mesophyll, Fig. 5. p), and below they 

 .an- joined to rather irregular and loosel) arranged cells (the 



