242 



FOUNDATIONS OF BOTANY 



diameters, then with a power of 200 diameters or more. Note the 

 structure of the filaments. Of what is each made up? Compare 

 with the structure of Oscillatoria. 



Move the slide so as to trace the whole length of several filaments, 

 and, if the unbroken end of one can be found, study and sketch it. 



Study with the higher power a single 

 cell of one of the larger filaments and 

 ascertain the details of structure. Try 

 to discover, by focusing, the exact shape 

 of the cell. How do you know that 

 the cells are riot flat? Count the bands 

 of chlorophyll. The number of bands 

 is an important characteristic in dis- 

 tinguishing one species from another. 

 Run in five-per-cent salt solution at 

 one edge of the cover-glass (withdraw- 

 ing water from the other edge with a 

 bit of blotting paper). If any change 

 in the appearance of the cell becomes 

 evident, make a sketch to show it. 

 What has happened to the cell-con- 

 tents? Explain the cause of the 

 change by reference to what you know 

 of osmose. 



On a freshly mounted slide run 

 under the cover-glass iodine solution, 

 a little at a time, and note its action 

 on the nucleus. Is any starch shown 

 to be present? If so, just how is it 

 distributed through the cell? 



276. Reproduction of Spirogyra. 

 The reproductive process in Spirogyra 

 is of two kinds, the simplest being a process of fission, or cell- 

 division. The nucleus undergoes a very complicated series of 

 transformations, which result in the division of the protoplasmic 

 contents of a cell into two independent portions, each of which is 

 at length surrounded by a complete cell-wall of its own. In Fig. 176 



FIG. 177. Process of Cell-Multi- 

 plication in a Species of Pond- 

 Scum. (Considerably magnified.) 



A, portion of a filament partly 

 separated at a and completely 

 so at b ; B, separation nearly 

 completed, a new partition of 

 cellulose formed at a; C, 

 another portion more magni- 

 fied, showing mucous covering 

 d, general cell-wall c, and a 

 delicate membrane a, which 

 covers the cell-contents b. 



