172 PRACTICAL BOTANY 



in transverse section, will be found embedded in the mesophyll : 

 the larger of these correspond in position to the swollen ribs of 

 the pinna. 



Note the endodermis as a continuous layer of cells, which com- 

 pletely surrounds the circular bundle, and within this the xylem 

 and phloem elements, similar to those of the stem : the bundles 

 show an approach to the collateral type, the xylem being 

 nearest to the upper surface of the leaf. 



XVI. Cut tangential sections (or strip off the epidermis) 

 from the upper and 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. 



b. The epidermis of the lower surface consists of cells 

 similar to the above : there are stomata with two guard-cells. 



The Sporangia. 



XVII. Having examined the sori as directed on p. 156 with 

 the naked eye or with a lens, cut transverse sections through 

 pinna? of leaves which bear sori, taking care that the sections 

 shall pass through one or more of them : mount as before, and 

 examine with a low power. Note 



1. The structure of the pinna, as above described. 



2. Opposite to, and seated upon a rib will be found the 

 membranous indusium, which, like an umbrella, covers over 



3. The sporangia, which are biconvex-lens-shaped, brown 

 stalked capsules, attached to the rib and filled with 



4. Numerous roundish, brown, unicellullar spores. 

 Observe more closely the structure of the single sporangium. 



It is composed of 



i. The stalk, which is of considerable length, and usually 

 consists of three rows of cells. Stalked glandular bodies are 

 often found as lateral branches on the stalk of the sporangium 

 in this species. 



ii. The capsule, which has the form of a biconvex lens, and 

 consists of a marginal series of cells with peculiarly thickened 



