62 



the archegonia, and is therefore the true 

 prothallium. Usually at this period the 

 megasporangium bursts, and the spores fall 

 to the ground, 

 (b) A few weeks after dissemination, free cell 

 formation begins in the remainder of the 

 spore cavity, and the whole space is filled 

 up by a large-celled tissue which is called 

 Endosperm. The megaspores now contain 

 both a prothallium and an endosperm. 



DEVELOPMENT OF AECHEOONIA. 



The archegonia are produced from the prothallium 

 thus : — 



(1) A superficial cell divides parallel to the 

 surface. 



(2) The upper of the two cells divides into four 

 cells by two walls at right angles to each other. 



(3) Each of these divides into two by an oblique 

 wall. In this way the neck is formed, consist- 

 ing of four rows, each two cells in thickness. 



(4) The lower of the first two cells sends out a 

 narrow prolongation between the neck cells ; 

 this becomes the canal cell of the neck — this 

 neck canal cell forces the neck cells apart. 



(5) The lower swollen portion cuts off a small cell 

 which is called the ventral canal cell and the 

 inferior large one the ovum or oosphere. 



(6) The two canal cells now become mucilaginous, 

 and the archegonium is ready for fertilization. 



