38 



PLANT STUDIES 



Fifi. 28. Ci^lls of tlic epidermis 

 of Marafita, sliowing tlie 

 iiiterlociciii^f walls, and a 

 BLoma (.V) witli its t\vi> giiaifl- 

 cells. 



a network of veins ; (2) a green substance (mesopliyll) in 



the meshes of tlie network ; and (3) over all an epidermis. 

 31. Stomata. — If a compound microscojie is used, some 



very important additional facts may l>e discovered. 'I'he 

 thin, transparent ejiidermis is 

 found to be made uji of a. layer of 

 cells which fit closely together, 

 sometimes dovetailing with each 

 other. Curi(nis ojx'iiiiigs in the 

 epidermis will also be discovered, 

 sometimes in very great numbers. 

 Guarding each opening are two 

 crescent-shajied cells, known as 

 guard-cells, and l)ctween them a 

 slit-like opening leads through the 

 e})idermis. The whole apiparatus 

 is known as a sfoiu/i (plural 

 stomata), which I'eully nu'ans 



"mouth," of which the guard-cells might be called the 



lips (see Figs. 2s, 2!)). Sometimes stomata, arc found only 



on the under side of the leaf, sometimes only 



on the upjjer side, and sometimes on both 



sides. 



The important fact about stomata is that 



the guard-cells can change their shape, aiul 



so regulate the size of the opening. It is not 



certain just how the guard-cells change their 



shape and Just what stomata do for leaves. 



They are often called " breathing pores," 



but the name is very inapproju-iate. Stomata 



are not peculiar to the epidtn-mis of foliage 



leaves, for they are found in the epidermis 



of any green part, as stems, young I'niit, 



etc. It is evident, tlieref<ire, that, they hold 



an important ridation to green tissue which 



is covered by epidermis. Also, if we examine 



