393 ELEMENTARY BIOLOGY. [CHAP. 



Both eventually come to rest, assume a globular shape, 

 lose their cilia and form a thick cell-wall around their pro- 

 toplasm, thus reproducing the vegetative condition of the 

 plant. 



Both kinds of zoospores are sensitive to light, swimming 

 towards the source of liglit, Avhen its intensity is moderate, 

 and away from it when its intensity is increased. 



For reasons similar to those which prove the vegetable 

 nature of Ton/la, Protococcus is a plant, although its zoo- 

 spores are curiously similar to the Monads among the lowest 

 forms of animal life. But it is now known that many of the 

 lower plants, especially in the group of Algce^ to which Pro- 

 tococcus belongs, also give rise to locomotive spores propelled 

 by cilia, like those of Protococcus, so that there is nothing 

 anomalous in the case of the latter. 



Like the yeast-plant, Protococcus retains its vitality after it 

 has been dried. It has been preserved for as long as two 

 years in the dry condition, and at the end of that time has 

 resumed its full activity when placed in water. The wide 

 distribution of Protococnis on the tops of houses and else- 

 where, is thus readily accounted for by the transport of the 

 dry Protococci by winds. 



LABORATORY WORI 



IV. 



A. Morphology. 



Vegetative stage. 



Spread out in water some mud from a gutter or 

 similar locality, and put on a cover-glass. Look for 

 the red or green Protococcus cells with a low power. 

 Having found some, put on a high power and make 

 out the following points. 



