370 



THE NON-VASCULAR PLANTS 



its parent, becomes more and more pronounced in the more 

 complex plants. 



Two other common green algae are Vaucheria and Spiro- 

 gyra. (See Figures i6y, i68, and 169.) Vaucheria forms 



dark-green, velvety masses. 

 It is much more coarse in 

 texture than Spirogyra, which 

 is the pale-green, slippery 

 pond scum. 



Vaucheria has no cross par- 

 titions in its filaments. Its 

 protoplasts appear to be 

 merged into one great proto- 

 plast with many nuclei. Such 

 a structure is called a coenocyte. 

 In Vaucheria the oogonia and 

 antheridia appear on special 

 branches. 



Spirogyra gets its name 

 from its large and beautiful 

 spiral chloroplasts. In it the 

 sex differentiation appears to be a differentiation between 

 individuals rather than between cells. Filaments lying 

 side by side produce short tubes which unite the cells lying 

 opposite each other. (See Figure 169.) The protoplasts 

 of one filament pass through these tubes and fuse with the 

 protoplasts of the other filament. From this behavior the 

 migrating protoplasts may be regarded as sperms and the 

 passive ones as eggs. Structurally, however, there appears 

 to be no difference between them. The filament which 

 loses its protoplasts may be regarded as a male individual, 

 and the receiving filament as a female individual. 



Fig. 167. — Vaucheria. Portion of a 

 filament bearing a branch on which 

 are three oogonia each containing a 

 fertilized egg. The antheridium, now 

 empty of sperms, appears as a droop- 

 ing, curved cell arising from the top 

 of the branch. 



