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TEXTBOOK OF BOTANY 



even years, and upon germination usually produces four motile spores, 

 each of which has the reduced number of chromosomes. A new filament 

 develops directly from each motile spore, and each of its cells has the 

 reduced number of chromosomes. 



Other common filamentous genera. Among the most widely distrib- 

 uted genera (Fig. 282) of pond algae is Spirogyra, with its usually 



KL L M 



Fig. 283. Reproduction in Spirogyra and inheritance of the chloroplast. 



spirally arranged, ribbon-like chloroplasts. Zygnema with stellate chloro- 

 plasts, and Motigeotia with a straight, ribbon-shaped chloroplast are al- 

 most as common. In the large group of algae represented by these three 

 genera, the cells are always cylindrical and there is a complete absence 

 of flagellate spores. Sexual reproduction is effected by the union of 

 gametes, one ( or both ) of which moves ameba-like to the other through 

 a conjugation tube ( Fig. 283 ) . The zygotes resulting from the union of 

 the gametes may remain dormant for several months or years. When they 

 germinate, new filaments develop from them. Reduction division occurs 

 at the first division of the zygote nucleus. 



The green felt-like Vaiicheria is very common in small streams and 



