THE ALG.E 



227 



213. Vaucheria : nutrition. Materials for food-making may 

 be absorbed from the moist earth or from the water in which 

 this plant grows. The abundant chlorophyll suggests con- 

 siderable ability to manufacture its own nutrient substances, 

 but this plant is not so 



well fitted for securing 

 abundant exposure to 

 light as is Cladophora. 

 It is to be noted that, 

 living on the land as 

 these plants often do, 

 they do not have the 

 protection against ex- 

 tremes of light and 

 temperature 

 that water 

 alg<e enjoy. 



214. Vaucheria: re- 

 production. As sug- 

 gested in section 212, 

 vegetative reproduc- 

 tion occurs in this 

 plant. Asexual repro- 

 duction may be started 

 by having the end of 



a branch cut off by a FIG. 177. Vaucheria 



cross wall. The part 



that is thus cut off 



proceeds to form a 



large reproductive body 



(fig. 177, J?, (7) ; the wall which surrounds it breaks, and 



after a period of swimming it germinates and forms a new 



plant (fig. 177, D). This special reproductive body is called 



a zoospore (animal spore), or swimming spore. The formation 



of zoospores may be induced in the laboratory by keeping 



Vaucheria plants in a dish of shallow water. 



A, branch of a vegetative plant ; B, branch form- 

 ing zoospore; z, young zoospore just emerging 

 from the sporangium (s) ; C, a free zoospore ; D, 

 zoospore germinating to form a new plant 



