GREEN ALGAE 



399 



and with no distinction of apex and base. They are slimy to the 

 touch, owing to their mucilaginous outer wall. Each filament is 

 partitioned by transverse septa into cells, each of which may be 

 detached from its neighbours by shock, when its convex ends demon- 

 strate its internal turgor. Growing on and dividing, each may form 



FIG. 337- 



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. (After Kny.) 



a new filament. Each cell is practically an individual (Fig. 337, cell h). 

 It is cylindrical, the proportion of length to breadth varying in 

 different species. Within the external wall is a layer of colourless 

 cytoplasm surrounding a central vacuole, in the middle of which the 

 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 species, may lie embedded 



