72 



THE ALGAE 



spores, and these then give rise to the germlings in which the erect 

 filament arises first and the prostrate portion subsequently or vice 

 versa. By increasing the osmotic pressure or by adding toxic salts 

 to the environment the thallus passes into a palmelloid state, whilst 

 imder other conditions akinetes can be formed. The plants are con- 



Fig. 37 Stigeoclonium. A, plant of S. tenue. B, basal portion of 

 5. lubricum. C, aerial portion of 5. protensum. D, rhizoids in S. 

 aestivale. E, palmelloid state. (A-C, E, after Oltmanns; D, after 



Fritsch.) 



fined to well-aerated fresh water though they have also been found 

 growing on fish living in stagnant water, but in these cases the 

 movements of the fish presumably provide adequate aeration. 



Chaetophoraceae: Draparnaldia (after J. P. R. Draparnaud). 

 Fig. 38 

 The plants, which are confined wholly to fresh water, are repre- 

 sented principally by the aerial system, the prostrate system being 

 entirely absent or else greatly reduced. The young plant is origin- 

 ally attached by means of a much reduced prostrate system to- 



