82 



Elementary Biology. 



corresponds to the male element, until movement of the 

 protoplasm of one of the cells takes place. Then, on the 

 general analogy that the male element is usually the more 

 active of the two (p. 52), we are able to guess that the more 

 passive cell is that which corresponds to the ovum. 1 



After undergoing a short period of rest, during which, no 

 doubt, various important rearrangements of the protoplasmic 

 materials take place, the body resulting from the union of 

 the two cells ('zygospore'), which has meantime obtained 

 a thick cell-wall, bursts first its own special capsule, and 



FIG. 22. GERMINATION OF Spirogyra jugalis. (Pringsheim.) 



I, 'zygospore' ; e,f, layers of cell-wall. II, germination of embryo, g: 

 III, young Spirogyra, with three cells already formed; c, cell-wall 

 of parent (female) cell ; /, ', new cell-walls ; c, conjugating processes. 



afterwards the mother cell-wall, and pushes out a long 

 filament, which develops gradually into a new Spirogyra. 



Such is the life-history of Spirogyra^ and it is to be 

 noted by way of recapitulation that we have here an 

 exceedingly simple thallus, producing two cells of different 



1 It is desirable that the student should as far as possible familiarise 

 himself with the terms in use in other text-books, after he has, by means 

 of a uniform terminology such as that adopted here, mastered the exact 

 signification of the various parts of plants, more especially of their re- 

 productive organs. 



