SWARM- SPORES OF VAUCHERIA. 



295 



Reproduction of Vauclieria Swarm-spores. From amongst 

 the acellular multinuclear Siphoneae we select for examination 

 the widely-spread Vaucheria sessilis in order to study the forma- 

 tion of its swarm-spores (zoospores) and also its sexual organs. We 

 can obtain swarm-spores of Vaucheria at any time if algae which 

 have for several days been kept bright and damp are flooded with 

 water, or if algae which have been cultivated in 0*2 to 0*5 per cent. 

 Knop's nutrient solution (see p. 251) in a bright position are trans- 

 ferred to pure water, or if cultures in water or in Ol to 0*2 per cent, 

 nutrient solution are placed in darkness. If we examine the cul- 

 ture with a lens of considerable focal length we can easily recognise 

 the first formation of the sporangia by the dark colour of the ends 

 of the threads. If now we seize with the forceps, at their point of 

 junction, a group of threads which appear to be in the desired 

 condition, and transfer them, without allowing them to be bent, 

 to an object-slide, we can study upon them direct the further pro- 

 cesses of development, 

 which, moreover, often 

 go on undisturbed un- 

 der the cover-glass, if 

 only the object is pro- 

 tected from its pres- 

 sure by thin sections of 

 elder - pith, or horse- 

 hairs, placed under its 

 edges. If a sporangium 

 is to be formed out of 

 the end of a branch, con- 

 tents rich in chlorophyll 

 collect in this, and the 

 end begins to swell club- 

 wise. The sap cavity is 

 constricted below the 

 end (Fig. 109, .4), and 



is soon separated off in 



FIG. 109. Vauchtria asstkf. A and B, formation 

 the upper part as a O f the sporangium ; C-E, formation of the swarm-spore 



snherical varuolp The out of tbe contents of the sporangium ; F, a swarm- 

 ricai \acuoie. ne spore ^ free . ,, a ^^on of the outer, colourless 



Sporangium is then CUt plasmic laver (ectoplasm) from the anterior end of the 



swarm^poVe. A-E (x 95) : F(x 250) ; G (x 450). 

 off by a partition wall, 



in the formation of which the chlorophyll-containing contents 

 of the young sporangium, and of the rest of the sac, temporarily 



