406 ELEMENTARY BIOLOGY. [CHAP. 



examining in a warm room the following morning. 

 In cold weather it is sufficient to put the vessel 

 containing the Spirogyra out-of-doors ; in summer 

 it may be surrounded with ice. 



In mounting the filaments to observe the di- 

 vision it is necessary to support the cover-slip by 

 means of two bristles or fragments of thin glass, so 

 that it may not press on the object. The higher 

 the power used the better. 

 II. Reproduction. 



1. Look out for masses of Spirogyra in which the fila- 

 ments are tangled, and of a dull-green colour, as 

 described in the text. These will generally be found 

 late in the summer, or at any time when the water 

 in which the plant is growing is getting low. 



2. Examine such filaments first with a low power, in 

 order to find the various stages of conjugation. 

 The details at each stage are then to be made out 

 with the high power. Observe 



a. Pairs of parallel filaments which have begun to 

 produce the lateral protrusion. Note that the 

 protrusions in the filaments are formed opposite 

 one another. 



b. Similar pairs in which the protrusions have al- 

 ready become continuous by absorption of their 

 walls at the point of contact, so that they now 

 form transverse tubes connecting the filaments. 

 Note that at this stage the cells of the one fila- 

 ment show a contraction of their contents, while 

 those of the other are unaltered. 



c. Stages in which the cell-contents of the one fila- 

 ment are passing over through the connecting 

 tubes into the cells of the other. 



