ALG7E. 



225 



or no chlorophyll (Fig. 159, B, a). From one part of the protoplasm of this antheridiiim- 

 cell are formed the numerous spermatozoids, very small long bodies with two cilia (D). 

 In several species the antheridia are curved like horns {F. sessilis, geminata, and 

 terrestris); in others they are straight (F. sericea) or curved sacs {F. pachyderma). The 

 Oogonia arise near the antheridia as thick protuberances (Fig. 159, A, B, og) filled with 

 oil and chlorophyll. They swell up into an ovoid form (usually oblique), and finally 

 the dense contents are separated by a septum from the base of the branch {F, osp). 

 The green and granular mass collects in the centre of the oogonium ; colourless proto- 

 plasm accumulates at its mouth, and withdraws from the cell-wall ; the cell-wall 







Fig. i^q.—Vaucheria sessilis; A, B origin of the antlieridium a on the branch b, and of the oogfonium og; C an open oogonium 

 expelling a drop of mucilage si; D spermatozoids ; E the spermatozoids collected at the mouth of the oogonium ; i^, « an empty 

 antheridiuni ; osp the oospores in the oogonium (A, B, E, F from nature, C, D after Pringsheim). 



suddenly opens and swells up into a jelly, and at this moment the contents are trans- 

 formed into an oosphere, contracting at the same time. In some species (as F. sessilis) 

 a colourless drop of mucilage is expelled from the mouth (C, si). At the same time 

 that the oogonium opens, the antheridium also bursts and allows the spermatozoids 

 to escape ; these press through the thin mucilage, on which they collect {E\ reach 

 the oosphere, mingle with it, and disappear. The oosphere appears then to assume 

 at once a sharp outline, and a double cell-wall may soon also be detected. The 

 oosphere has transformed itself into an oospore; its chlorophyll assumes a red or 

 brown-red colour, and the cell-wall thickens, so that three layers may generally be. 

 distinguished in it (Fig. 159, F, osp, the oospore in the oogonium). The formation of 

 the oogonia and antheridia begins in the evening, and is completed the next morning ; 

 fertilisation is accomplished between 10 and 4 in the day. 



In their processes of vegetation several other genera approach very near to Vaucheria, 

 especially Botrydium. The young plant is (according to A. Braun : Rejuvenescence, 

 p. 128) a spherical Protococcus-like cell ; subsequently a hyahne prolongation is formed 

 below which branches like a root and penetrates the earth, while the upper part swells up 

 into an ovoid vesicle, in which the protoplasm forms, with the chlorophyll-grains, a 

 parietal layer. From this arise, after the growth is matured, a number of zoospores 



Q 



