72 



The mother cells round themselves off, and eacii 

 produces four spores tetrahedi ally. The spores 

 float about in the sjporangium in the material formed 

 by the disintegrated tapetal cells. 



Dehiscence. One layer of the sporangium 

 becomes fibrously thickened. This layer stands out 

 as a ridge, and is called the annulus ; the wall of the 

 sporangium dries up, the annulus contracts and rup- 

 ture takes place at the weakest part. In this way the 

 spores are liberated. 



OOPHYTE OR SEXUAL GENERATION. 



Germination of a Spore. The exospore splits, 

 and the endospore forms a germ-tube, into which 

 passes the nucleus of the s^^ore. This germ-tube 

 produces a small, green, heart-shaped body, called 

 the Prothallium, the growing point of which lies in 

 the depression. Later on, a cushion of tissue is 

 formed just behind the apex. The prothallium con- 

 tains chlorophyll in abundance, and is attached to 

 the substratum by numerous rhizoids, or root-hairs. 

 It has thus an independent existence. On the under 

 surface are i^roduced the sexual organs. The male, 

 called antheridia, appear among the root-hairs at the 

 posterior end, i.e , on the unicellular portion of the 

 prothallium. The female, called arcJie.gonia. appear 

 on the thickened portion just behind the apex. 



Antheridia. Each antheridium which projects 

 beyond the surface as a dome-shaped structure, 



