70 



MORPHOLOGY OF THE CELL. 



238. Stomata. 



can be plainly seen, thus affording opportunity for examining 

 the movements of protoplasm, and for the study of the e fleets 

 of reagents upon the contents of cells. 



Young hairs contain much protoplasmic matter ; at a later 

 stage the} r have a large proportion of cell-sap ; still later many 

 are filled onlv with air. 



*.' 



237. At first the epidermis is alvvaj'S completely continu- 

 ous, the cells being in close contact with each other ; but 

 soon there appear, especially in leaves, guarded openings 

 through which the interior of the plant is brought into com- 

 munication with the surrounding atmosphere. These apertures 

 are of two principal kinds, the most important and widely dis- 

 tributed being 



These are combinations of epidermal cells of 

 a peculiar character, between 

 which a narrow slit extends 

 directly through the epidermis 

 to an intercellular space be- 

 low. The cells bordering the 

 slit are well termed guardian 

 cells, on account of their 

 opening and closing under 

 certain circumstances. The 

 neighboring epidermal cells 

 are frequently arranged in a 

 definite order ; and the po- 

 sition of the stoma has in 

 man} 7 cases a plain relation to the underlying framework. 



Stomata belong especially to green organs exposed to the air ,- 

 but they have been detected on all superficial parts of the plant, 

 with the exception of roots. 1 



239. Viewed from above, stomata appear generally as elliptical 

 bodies through which runs a narrow slit in the direction of the 

 longer diameter. Each guardian cell is therefore half the ellipse. 

 The cleft varies in width according to certain external condi- 



50 



51 



1 The following cases are cited by de Bary (Vergl. Anat., p. 49) : On rhizo- 

 mata and tubers (young potatoes), on the perianth, the anther (in Lilium 

 bulbiferum), on the pistil, on the seed-coat (Canna). Plants destitute of chloro- 

 phyll may also be destitute of stomata, as in Monotropa Hypopitys ; or have 

 them only on the pistil, as in Lathrsea. 



FIG. 50. Adult stoma of Hyacinthus orientalis, seen from above. (Strasburger.) 

 FIG. 51. The same, seen from below. 



