50 



REPRODUCTION 



4. Spirogyra. Of the thread-like green algae that we 

 find in our ponds this is one of the most beautiful. The 

 pupil should see it under the microscope, if possible. It 

 is a chain of elongated cells joined end to end. The green 

 matter (chlorophyll) is arranged in one or more strikingly 

 regular spiral bands. This is a perfect cell with nucleus, 

 protoplasm, and all the cell organs. As in cells generally, 



these have been 

 formed by the di- 

 vision of mother 

 cells. The whole 

 filament of cells 

 came by division 

 from one cell. 

 When the right 

 time comes, two fil- 

 aments that are ly- 

 ing side by side 

 send out from their 

 various cells short 

 branches. Each of 

 these branches 

 grows and unites 

 with a branch from 

 the nearest cell in 

 the other filament. 

 When they meet, 

 the partition dis- 

 solves at the point 

 of union, and the 

 cavities of the two 

 cells are thus put 

 into communica- 

 tion. A little later 

 Figure 12. Spirogyra as viewed under the the protoplasm of 

 microscope. The figures at the right show the pro- qj^^ Qf these cells 



cess of conjugation. F7-o7n Coulter's Plant Life ayid 

 Plant Uses. 



flows through this 



