9 8 



MORPHOLOG Y. 



ing cells, and the supplying cell may be the smaller, this is not general. We 

 say, therefore, that there is no differentiation among the gametes, so that 

 usually before the protoplasm begins to move one cannot say which is to be 

 the supplying and which the receiving gamete. 



231. Position of the plant spirogyra. From our study then we see that 

 there is practically no differentiation among the vegetative cells, except 

 where holdfasts grow out from some of the cells for support. They are all 

 alike in form, in capacity for growth, division, or multiplication of the 

 threads. Each cell is practically an independent plant. There is no differ- 

 entiation between vegetative cell and conjugating cell. All the cells are 

 potential gametes. Finally there is no structural differentiation between the 

 gametes. This indicates then a simple condition of things, a low grade of 

 organization. 



232. The alga spirogyra is one of the representatives of the lower algae 

 belonging to the group called Conjugatce. Zygnema with star-shaped chloro- 

 plasts, mougeotia with straight or sometimes twisted chlorophyll bands, be- 

 long to the same group. In the latter genus only a portion of the protoplasm 

 of each cell unites to form the zygospore, which is located in the tube between 

 the cells. 



Fig. 90. 

 Micrasterias. 



Fig. 91. 

 Xanthidium. 



Fig. 89. 

 Closterium. 



Fig. 92- 

 Staurastrum. 



Fig. 94. 

 Cosmarium. 



233. The desmids also belong to the same group. The desmids usually live 

 as separate cells. Many of them are beautiful in form. They grow entangled 

 among other algae, or on the surface of aquatic plants, or on wet soil. Sev- 

 eral genera are illustrated in figures 89-94. 



