900 



ELEMENTS OP BOTANY. 



free. It may be found flourishing in unfrozen springs, even in mid- 

 winter. 



271. Examination with the Magnifying Glass^ — Float a little of 

 the material in a white plate, using just water enough to cover the 

 fcottom of the latter. Study with the magnifying glass and note the 

 green color of the threads and their great length as compared with their 

 thickness. Are all the filaments about equal to each other in diameter ? 

 Handle a mass of the material and describe how it feels between the 

 fingers. 



272. Examination with the Microscope. — Mount 

 in water under a large cover-glass and examine first 

 with a power of about 100 diameters, then with a 

 power of 200 diameters or more. Note the struc- 

 ture of the filaments, each made up of a row of cells 

 placed end to end. 



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 make out the details of 

 structure shown in Fig. 192. Try to ascertain, by 

 focusing, the exact shape of the cell. Count the 

 bands of chlorophyll. The number of bands is an 

 important character in distinguishing one species 

 from another. 



Run in five-per-cent salt solution at one edge of 

 the cover-glass (withdrawing 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- 

 contents ? Explain, by reference to what you know 

 of osmose, the cause of the change. 



On a freshly mounted slide run in iodine solu- 

 a little at a time, and note its action on the nucleus. Is any starch 



Fig. 192. —Cell from a 

 Thread of Pondscum 

 {Spirogyra). (Magni- 

 fied about 90 diame- 

 ters.) 



Ic, nucleus ; ch, spiral 

 band containing 

 chlorophyll; p, 

 pyrenolds, little 

 masses of proteid 

 material with 

 starch-grains. 



tion. 



shown to be present ? If so, just how is it distributed through the cell ? 

 273. Beproduction of Spirogyra. — The reproductive process in 

 Spirogyra is of two kinds, the simplest being a process of fission, not 

 unlike that with which the student has become familiar in Protococcus. 

 The nucleus umlergoes a very complicated series of transformations. 



1 Consult Huxley's liloUxjif and Spalding's Introduction to Botany. 



