152 



FOUNDATIONS OF BOTANY 



p. 



A 



somewhat kidney-shaped and become more or less curved 

 as they are fuller or less full of water (see Sect. 170). 



162. Calculation of Number of Stomata per Unit of Area. 

 In order to get a fairly exact idea of the number of 

 stomata on a unit of leaf-surface, the most convenient 



plan is to make 

 use of a photo- 

 micrograph. The 

 bromide enlarge- 

 ment No. 12 of 

 the Tower series 

 represents about 

 a twenty-five- 

 hundredth of a 

 square inch of the 

 lower epidermis of 

 the cyclamen leaf, 

 magnified until it 

 is about fifteen 

 inches square. 

 Count the number 

 of stomata on the 

 entire photograph, 

 then calculate the 

 number of stomata 

 on a square inch 

 of the surface of 

 this leaf. If a cyclamen plant has twelve leaves, each 

 with an average area of six square inches, calculate the 

 number of stomata of the lower epidermis of all the leaves 

 taken together. 



st 



PIG. 117. Epidermis of Leaf of Althaea. 



(Much magnified.) 



A, from upper surface ; S, from lower surface. 

 h, star-shaped compound hairs ; st, stomata ; p, 

 upper ends of palisade-cells, seen through the 

 epidermis ; e, cells of epidermis. 



