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A TEXTBOOK OF THEORETICAL BOTANY 



Antherozoids 



I 



Fig. 367. — Chora fragilis. Section of a mature anther- 

 idium, showing antherozoids coiled in the cells of 

 the spermatogenous filaments. 



The Oogonium 



In many species the same basal cell of the node which gave rise to the 

 antheridium may also give rise to the oogonium. This cell divides into 

 two, the lower being the nodal cell and the upper the oosphere (Fig. 368). 

 From the periphery of the nodal cell five segments are cut off, forming a 

 group of cells which grow outwards and upwards till they envelop the 

 oosphere. The oosphere elongates and becomes oval in shape, while these 

 enveloping cells keep pace with its growth. Meanwhile these cells each 

 divide into two by cutting off at the top a cell, which together form a tier of 

 five cells, termed the coronula. 



At the same time the oosphere has cut off below a basal cell, which is 

 termed the turning cell. With the aid of this turning cell the oosphere 

 rotates so that the enveloping cells, which are adherent to it at the top, are 

 spirally twisted, always in a clockwise direction (Fig. 369). The enveloping 

 cells thus serve as a protective tissue around the oosphere, though it is 

 difficult to see the purpose of the spiral twisting unless it be to tighten their 

 contact with the cell inside and with each other. Gelatinous material appears 

 at the top of the oogonium, between the cells of the coronula and the oosphere, 

 and it may be that the twisting movement assists in its extrusion. 



Shortly before fertilization the inner walls of the enveloping cells become 

 dilated and push the cells of the coronula apart, thus leaving a narrow neck 

 down which the antherozoids find their way. The wall of the oosphere 

 becomes gelatinous, and the nucleus of the antherozoid, after entry, fuses 



