as a hypnosporangium ; it is about '5 mm. 

 in diameter, and is dark olive green in 

 colour, and possesses a thick cell wall. 

 These hypnosporangia, if kept dry, may 

 remain unchanged for a long time, but if 

 placed in water they develop zoospores at 

 once. 



SWARMSPORES. 



The swarmspores or zoospores can move very rapidly 

 through the water by means of the single anterior ciliam. 

 They are sensitive to the light, being attracted towards it 

 when it is not too strong, but are repelled by an intense 

 light. The result of these movements is that when they 

 come to rest the zoospores are in a position to make use 

 of the light for the process of assimilation, and are able 

 to provide themselves with a cell wall and develop into 

 new plants. 



The germination of the zoospores, whether derived from 

 ordinary sporangia (i) (2), from root-cells (3«), or from 

 hypnosporangia (3c) is the same. When the zoospore 

 comes to rest it rounds itself off and increases in size ; the 

 chromatophores and nuclei increase in number by division, 

 and the plant puts out a delicate rhizoid which remains 

 unbranched for some time. The upper green part may, 

 however, become branched, sometimes very considerably. 

 In this condition the plant is capable of further develop- 

 ment in several different ways, according to the environment. 



I. It may reproduce itself vegetatively by budding. 



A new vesicle grows out from the aerial part of 



the plant, which puts out rhizoids into the earth 



and finally becomes isolated from the mother plant. 



II. If the small vegetative plants be placed in water 



the contents become divided up into zoospores. 

 III. The young vegetative plants gradually develop into 

 ordinary plants with branched rhizoids — especially 

 if they are grown on damp clay and not too 

 crowded together. They ultimately produce zoo- 

 spores, as described in i, 2, and 3. 



