GREEN ALGAE 



373 



single nucleus is suspended by colourless threads. The most marked 

 feature is the green spiral chromatophore, which gives the genus its 

 name. One or more of these, according to the species, may lie embedded 

 in the peripheral cytoplasm, coiled corkscrew-fashion. As in the 

 Conjugales generally, pyrenoids occur in the chromatophores : they 



Fig. 277. 



Two filaments of Spirogyra, which illustrate various stages of conjugation, a, b, 

 have formed outgrowths which have met at c ; the protoplast d is contracted to a 

 dense sphere. The next lower pair of cells show conjugation, the protoplasts 

 fusing at /. In g, conjugation is complete, a zygote having been formed by the 

 fusion of two protoplasts, h shows a cell not in conjugation. (After Kny.) 



are highly refractive, and form centres for the formation of starch, 

 while the threads that suspend the nucleus usually run out to them. 



Vegetative propagation is simply by division of the cells, which 

 occurs during the night, and may be continued indefinitely. As the 

 season progresses the filaments conjugate. Adjacent filaments put 

 out processes from cells opposite one another, which meet, flatten, 

 and fuse at their tips, the intervening wall being absorbed. Their 



