Lecture XV. 117 



Usually a large number of tetrasporangia are formed in a branch 

 which becomes distorted and nodular as they mature. 



The tetraspores on their escape float passively in the water. 

 When they settle on a suitable support they adhere to it and form 

 round themselves a cell-wall. The wall in contact with the support 

 is sucker-like and fixes the germinating spore. A transverse 

 division establishes an apical cell and immediately initiates the 

 characteristic growth of the plant. 



The sexual reproduction of Polysiphonia presents many features 

 of interest. The sperm cells are not provided with cilia ; they are 

 developed in large numbers in special organs the antheridia, 

 which arise in the same manner as the hairs. Unlike these, how- 

 ever, at an early stage one of the branches of the hair develops a 

 cortex. From the cortical cells numbers of small cells are de- 

 veloped. They are produced like the cells of short bifurcating 

 filamentous hairs, but so closely crowded together that they form 

 a compact tissue-like mass. Their terminal cells form the super- 

 ficial layer of the club-shaped antheridium, which is attached to 

 the axis by the basal part of the hair. When mature, the proto- 

 plasmic contents of each superficial cell emerges as a naked cell 

 and is borne about by the currents in the water. 



The female gamete is called the carpogonium. It too is the 

 terminal cell of a lateral hair, which is developed from a cortical 

 cell of a branch. Immediately after the differentiation of the 

 cortex of a filiform branch, one of its cells divides longitudinally 

 into an inner and an outer segment. The outer segment sub- 

 divides and develops into a short filament of four cells the carpo- 

 gonial hair (often called branch), which turns upwards so as to be 

 almost parallel to the row of axial cells. The terminal cell of this 

 branch produces a long process while its base is enlarged so that 

 the cell may be compared to a flask with a long and very slender 

 neck. This cell is the carpogonium. The filiform process is called 

 the trichogyne. The inner segment of the cortical cell now divides 

 transversely into two, one of these, the upper portion, is called the 

 auxiliary cell. It is approximately at the same level as the base of 

 the carpogonium. Meantime the cortical cells at each side of the 

 carpogonial hair develop and subdivide, giving rise to short fila- 

 ments of cells which grow round the carpogonial hair, envelop it, 

 and converge on its outer side. These filaments cohere together 

 and form a spherical receptacle coating over the carpogonial hair 

 while they allow the trichogyne to project through a minute gap 

 between them. This whole structure, attached by the base of the 

 branch on which it has developed, is called a procarp. Usually 



