Lecture XL 87 



The assimilated materials are also utilised for the production of 

 new individuals. 



The reproduction of Vaucheria is characteristically effected by 

 an asexual and a sexual method. 



In the asexual method the terminal mass of protoplasm of one 

 of the ends of the branches becomes cut off from the rest of the 

 coenocyte by a partition of cellulose. The chamber thus cut off 

 is distended into an ovoid form, possibly owing to an increase in 

 the osmotic pressure of the vacuole enclosed in the isolated mass 

 of protoplasm. Within the inner zone of the cytoplasm of this 

 portion the nuclei marshal themselves with great regularity so 

 that they are equally spaced from one another and are only one 

 deep. Outside them the chloroplasts lie in the peripheral cyto- 

 plasm. With this arrangement of its parts the protoplasm con- 

 tracts a little and draws away from the wall, and forms a rounded 

 mass lying free within the ovoid chamber. Cilia now appear on 

 the surface of this mass, a pair radially opposite each nucleus, and 

 by their lashing motions cause the mass to rotate in the chamber. 

 The wall forming the distal end of the latter partially dissolves 

 and a hole is formed, which the motile mass within is not long in 

 finding out. Usually the hole is too small to allow this mass, 

 which is called a zoospore, to pass through with ease, and the 

 zoospore has to undergo considerable distortion before it escapes. 

 Sometimes in its struggles to be free, when part of it has already 

 emerged the remainder is detained by the constriction formed by 

 the opening, the zoospore parts in twain and the anterior swims 

 away leaving its less fortunate half to emerge later. 



The zoospore swims about for perhaps 15 minutes. During 

 this time it is positively phototropic, i.e. it acts just like Volvox 

 and swims towards the light, but it is also apparently sensitive to 

 other stimuli, for its course is seldom exactly defined by the 

 direction of the light. At the end of this time its motions become 

 sluggish and ultimately it comes to rest. It casts off its cilia and 

 secretes a cell-wall. The cell-wall is at first ovoid, enclosing an 

 egg-shaped mass of protoplasm. The latter is deep green in 

 colour owing to the presence of large numbers of chloroplasts. 

 If conditions are favourable the protoplasm within soon begins 

 to grow and pushes out into a tubular plant covered with the 

 cell-wall which keeps pace in its growth. Rhizoids and 

 branches appear in due course and thus a new individual is 

 established. 



Sexual reproduction is also found in Vaucheria. Special 

 branches are formed on the ccenocyte to carry out this process. 



