THE ALG.E 



171 



-ch 



- -n 



by side. The cells of each filament send out lateral 

 outgrowths, which exactly correspond to each other in 

 position. These outgrowths come into contact, and 

 adhere together; the walls separating them are then 

 absorbed, so as to leave an open passage between the 

 opposite cells of the two threads (see Fig. 72). 



The contents of the cells in 

 one of the two filaments now 

 contract, receding from the 

 cell-wall, and round them- 

 selves off ; for a time the cells 

 of the other filament remain 

 unchanged. The contracted 

 cell-contents next begin to 

 insinuate themselves into the 

 connecting passage, and gradu- 

 ally work through it, passing 

 into the opposite cell (Fig. 

 73). They then unite with 

 the contents of the latter, 

 which in the mean time have 

 themselves somewhat con- 

 tracted. 



In this case the fusion of 

 the nuclei of the two conjuga- 

 ting cells has been observed. 

 The united protoplasmic mass 

 assumes a rounded or oval 



form, and surrounds itself with a cell-wall, which becomes 

 thickened and cuticularised on its external surface. It has 

 been shown that in some species at any rate the chloro- 

 plast or chloroplasts of the active cell disintegrate in the 

 zygospore, so that those of the new generation belong 



FIG. 72. Spirogyra longala 

 conjugating. The two parallel 

 filaments are putting out the 

 conjugating outgrowths (a), 

 which at b are already in con- 

 tact ; ch, spiral chloroplastid ; 

 n, nucleus, with radiating 

 protoplasmic fibrils. Magni- 

 fied about 350. (After Sachs.) 



