20 THK PLANT CELL. 



make up for any deficiency in strength of the epidermis (see 

 Figs. 8 and 10). 



In surface view epidermal cells present a variet)' of stiapes; 

 thus they may be rectangular, polyhedral, or sinuous in contour 

 (see Fig. 11). In all cases, however, a regular pattern is 

 preserved, the component cells fitting close so as to leave no 

 intercellular spaces, except vchere stomata occur. 



In section, some epidermal cells may show minute perforations 

 or " pits " in their inner walls. These pits have been functional 

 in permitting of the passage of the protoplasm from the epidermis 

 into the deeper cells just internal to it when the work of the 

 li-sing substance has been completed ; they may be seen in the 

 epidermal cells of Smila.i: 



Fig. II. — Epidermal Cells hf Seitnni, seen in surface view. 



Note. — Epidermis maybe studied in any of tlie higher plants. Great 

 thickening of the outer wall may be seen in the epidermal cells of 

 the Holly leaf, and of Vi«cum album, leaf of Piniis sylveslris, and Ficus 

 elastica. The cuticle may be caused to separate by the use of' caustic 

 potash ; and by the use of Schulze's solution, the part of the wall which 

 still remains unaltered cellulose may be distinguished from the rest. 



2. Structures to be observed in connection with the Epidermis. 



These are : — 



(a) Stomata (occurring in leaves, petioles, petals, and some stems). 



(b) Hairs, of varied shape, size, and function. 



(a) Stomata are apertures or intercellular spaces occurrini' at 

 certain points in the epidermis, which permit of the passage of 

 the gases of the atmosphere into spaces surrounded by tha 



