282 



ALG^E 



of a branch is cut off by a septum as a zoospoi-ange ; the dark green en- 

 dochrome in it gradually contracts into an ellipsoidal form, finally forcing 

 its way out by the rupture of the cell-wall at the apex of the branch. 

 The rotatory motion imparted to the zoospore by its fringe of cilia 

 begins even within the mother-cell. During its escape it sometimes 

 gets nipped in two by the pressure of the cell-wall, and each half then 

 becomes a zoospore, one inside, the other outside, the wall of the 

 mother-cell. The zoospores are formed in the night and escape in the 

 morning ; their spontaneous motion lasts for a period varying from less 

 than a minute to several hours. As soon as they have come to rest they 







Fig. 248. — Vaucheria sessilis Vauch. A, B, formation of antherids and oogones ; k, male 

 branch ; a, antherid ; og, oogone. C, oogone opening and ejecting drop of mucilage, si. 

 D, antherozoids. I£, antherozoids entering oogone. F : a, empty antherid ; osp, oogone 

 with fertilised oosperm (magnified). (After Pringsheim and Goebel.) 



lose their cilia, and become invested by a cell-wall of cellulose ; their 

 germination begins during the same day or the following night. The 

 spore puts out either one or two germinating tubes, formed by its inner 

 coat or endospore bursting through the outer coat or exospore ; and 

 the new plant usually fixes itself by a rhizoid or root-like organ of 

 attachment. 



The sexual reproductive organs of Vaucheria, oogones and antherids^ 

 originate as lateral protuberances on a filament, sometimes even on 



