n8 



BOTANY. 



to find cells which have the protoplasm in some of these different 

 stages. When the zygospores are being studied one should 

 look for some cells in these stages. 



\=\ ]— 



Fig. t)4. 



Conjugation in spirogyra; from left to right beginning in the upper row is shown the 



gradual passage of the protoplasm from the supplying cell to the receiving cell. 



203. The zygospore. — This zygospore now acquires a thick wall which 

 eventually becomes brown in color. The chlorophyll color fades out, and a 

 large part of the protoplasm passes into an oily substance which makes it 

 more resistant to conditions which would be fatal to the vegetative threads. 

 The zygospores are capable therefore of enduring extremes of cold and dry- 

 ness which would destroy the threads. They pass through a " resting'' 

 period, in which the water in the pond may be frozen, or dried, and with the 

 oncoming of favorable conditions for growth in the spring or in the autumn 

 they germinate and produce the green thread again. 



For further reading on spirogyra and its relatives see the 

 author's larger " Elementary Botany," Chapter XV. 



