i64 A TEXTBOOK OF THEORETICAL BOTANY 



grows out to form the trichogyne, while the lower part of the cell enlarges 

 as the carpogonium. 



Antheridia 



M^ 



STALK CELL 



SPERM 



MOTHER CELL 



SPERMATIUM 



■.'>^^ 



Fig. 153. — Polysiphonia fastigiata. Branches bearing antheridia. 



The spermatia are borne passively to the trichogyne and the male nucleus 

 enters and passes down it, finally fusing with the carpogonial nucleus, which 



lies at the base of the carpogonium. 

 Then the trichogyne shrivels up and 

 disappears. 



The processes which follow fertiliza- 

 tion are complex and differ considerably 

 in different species. We will first take 

 as a type one of the simpler examples, 

 Polysiphonia nigrescens, which is a com- 

 mon British species. 



The basal cell of the procarp branch, 

 which is known as the supporting cell, 

 cuts off" upwards a new cell which is 

 called the auxiliary cell (Fig. 155). 

 This cell becomes attached to the car- 

 pogonium by a wide protoplasmic con- 

 nection. The fertilized diploid nucleus 

 of the carpogonium now divides and one 

 of the daughter nuclei passes over into 

 the auxiliarv cell. A wall is formed cut- 

 ting it off" from the carpogonium, which 

 later withers. 



In the auxiliary cell there is already 

 its own monoploid nucleus, which, however, soon disappears. The diploid 

 nucleus from the carpogonium divides and one nucleus enters a branch of 

 the auxiliary cell, which becomes the primary cell of a gonimoblast. 



AXIAL 

 SIPHON 



CENTRAL 

 SIPHON 



Fig. 154. — Polysiphonia violacca. Struc- 

 ture of the antheridial branch. {After 

 Yamanouchi.) 



