Lecture IX. 7 1 



jugation-tube," as it is called. As soon as the two masses of 

 protoplasm run together in the conjugation-tube the protoplasm 

 remaining in the cells begins to draw away from the cell-walls, 

 apparently by a reduction in the size of the vacuoles. The 

 retraction is much more marked in one of the pair than in the 

 other, and finally the protoplasm evacuates it entirely and is 

 drawn over and passes through the conjugation-tube into the 

 other cell. In this cell the total protoplasm of the two cells, 

 cytoplasm, nuclei and chloroplasts, fuses to form an egg-shaped 

 mass. A strong cell-wall is secreted round this compound 

 mass, or zygospore as it is called, and a period of rest is entered 

 upon, during which the zygospore often remains enclosed in 



A B C D 



FIG. i2.Spirogyra porticalis, conjugating cells, x 125. A, beginning of 

 the formation of the conjugation processes ; B, processes in contact ; 

 C, conjugation-tube completed by solution of end-wall of processes, 

 fusion of the two cells effected, male cell is seen passing into the female 

 cell ; D, zygospore lying in the female cell-wall. 



the original wall of the conjugating-cell. At the end of its 

 rest the outer layer of the zygospore's wall gelifies at one point 

 and a tubular extension of the inner layer is thrust out, thus 

 converting the egg-shaped zygospore into a more nearly cylindrical 

 cell. The protoplasm within thus obtains space to distend itself 

 and the chloroplast to unravel till the zygospore gradually as ? 

 sumes the appearance of an adult cell of Spirogyra. As it 

 elongates it ruptures the enclosing cell-wall of the original con- 

 jugating-cell. At first one end of the young plant, or embryo, 

 is very often narrower than the other and into it the chloro- 

 plast does not extend. This narrow, colourless end or process 

 takes on the function of a sucker and attaches the embryo to 

 solid objects. Soon, however, cell-division produces a filament 



