MALE FERN. SPORANGIA. 203 



pass through one or more sori. 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, unicellular 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 

 thickened walls, which constitute the ring 1 , and thinner- 

 walled, flattened cells, which together form the lateral 

 walls of the completely closed sporangium. 



Note sporangia in which the lateral walls have been 

 ruptured transversely, the ring having straightened 

 itself out with sufficient force to tear the more delicate 

 lateral walls : by this means the spores are liberated. 



Examine single spores under a high power ; they are 

 unicellular bodies, having a brown wall, with external 

 band-like outgrowths of the exospore or outer layer of 

 the wall. All the spores are alike (Homosporous). 



The various stages of development of the sporangium may be 

 found in any sorus in which only the first sporangia have come 



