632 A TEXTBOOK OF THEORETICAL BOTANY 



originate from the cytoplasm of the mother cell. They are attached to a 

 narrow band, the blepharoplast, which lies against the anterior end of the 

 antherozoid (Fig. 641). The antherozoid is very similar to that of the Ferns 

 in structure and appearance, and is especially like that of Osmiinda. 



Development of the Archegonium 



The archegonia arise on a cushion-like part of the large prothallus, and 

 as fresh lobes are formed additional archegonia may be formed at their bases. 

 At first the archegonia point downwards, as they do in the Fern, but by 

 subsequent development of fresh lobes they become turned upwards (Fig. 

 642). The development of the archegonium is similar to that in the Fern, 



Archegonium neck 



Oosphere 



Fig. 642. — Eqiiisetmti arvense. Prothallus with 

 archegonia. 



though usually no basal cell is formed. The mother cell of the archegonium 

 divides into a central cell and a neck cell. From the central cell two neck- 

 canal cells are cut off above and a ventral cell below, whilst the neck cell 

 divides into three or four rows each consisting of four cells. The uppermost 

 neck cells are long and bend back, leaving a wide opening for the entrance 

 of the antherozoid. Lastly, the ventral cell divides obliquely to give the 

 ventral canal cell and the oosphere. 



Development of the Embryo 



Fertilization is effected in the same way as in the Ferns by the migration 

 of the antherozoid down the neck of the archegonium, followed by the fusion 

 of the two gamete nuclei to form an oospore. Several archegonia on one 

 prothallus may be fertilized and develop simultaneously. 



The oospore divides into two by a horizontal wall, after which the upper 

 cell divides, forming the initial cells of the first leaf and of the young stem. 



