274 



ALGsE 



FIG. -z^.Cladophora. gracilis Ktz. a, natural size 

 l>, upper, c, lower portion (x 200). (After Hauck.) 



genera, vegetative propagation 

 takes place by means of resting- 

 spores or cysts, usually found 

 in swollen barrel-shaped cells. 

 In Conferva the resting-cells 

 may be either akinetes or apla- 

 nospores ; and Wille believes 

 that they are produced espe- 

 cially under circumstances un- 

 favourable for the formation of 

 zoospores. The resting-spores 

 of Confervacese are formed in 

 three different ways: either (i) 

 by rejuvenescence, and the for- 

 mation of a new cell-wall round 

 the contracting contents; or (2) 

 by separation of a portion of the 

 cell-substance so as to form a 

 swollen part of the mother-cell,, 

 and the thickening of the cell- 

 wall at this portion; or (3) by 

 the simple thickening of the 

 wall of the mother-cell. In the 

 formation of aplanospores, one, 

 two, or four proceed from a 

 single cell by the cell-contents 

 rounding off and enclosing 

 themselves in a cell-wall while 

 still within the parent-cell. They 

 hibernate within the parent-cell, 

 and germinate in the spring. 

 Resting swarm - cells^ naked 

 masses of protoplasm endowed 

 with an amoeboid power of mo- 

 tion, are formed in the same 

 way. 



The mucilaginous sheath of 

 the Confervaceae appears to 

 have the same construction as 

 in the classes of algae already 

 described, but is often but feebly 

 developed. Wille states that the 



