202 PRACTICAL BOTANY. 



note the form of the two Guard-cells as seen in 

 transverse section, and their position in relation to 

 the epidermis. 



4. Here and there Vascular bundles, of circular 

 appearance in transverse section, will be found em- 

 bedded in the mesophyll : the larger of these correspond 

 in position to the swollen ribs of the pinna. 



Note the Bundle-sheath as a continuous layer of 

 cells, which completely surrounds the circular bundle, 

 and within this the xylem and phloem elements similar 

 to those of the stem : the bundles show a tendency to 

 the collateral type, the xylem being nearest to the 

 upper surface of the leaf. 



XVIII. Cut tangential sections (or strip off the 

 epidermis) from (a) the upper, and (ft) the lower surface 

 of the leaf : mount as before, and compare them. 



(a.) The epidermis of the upper surface will be 

 found to consist of cells with sinuous outline, and 

 protoplasmic contents, with chlorophyll : no stomata 

 will be found. 



(5.) The epidermis of the lower surface consists of 

 cells similar to the above; there are stomata with 

 two guard-cells. 



The development of these stomata may be studied with ad- 

 vantage in young leaves, by stripping off the epidermis, or by 

 cutting tangential sections. Special attention may be given to 

 the peculiar case of Aneimia. 



The, Sporangia. 



XIX. Cut transverse sections through pinnae of leaves 

 which bear Sori, taking care that the sections shall 



