i PRACTICAL EXERCISES 29 



1. The cell-wall will not be appreciably altered or 



stained. 



2. The film of protoplasm (primordial utricle) will 



have stained a pale yellow or brown, and may 

 often be seen to have separated partially or 

 completely from the cell- wall, from which it 

 may now be readily distinguished. 



3. The chromatophores will have assumed an in- 



definite dusky colour, while the pyrenoids will 

 be a dark purple. 



4. The nucleus will have stained a deep yellow or 



brown, and inclosed within it one or sometimes 

 two nucleoli may be recognized by their 

 deeper colour, and high refractive power. 



b. Irrigate afresh specimen with 2J per cent, solution 

 of common salt, and watch the result, which will take 

 some minutes to appear. The protoplasm will gradually 

 separate from the cell- wall, and while the latter retains 

 its form and position, the protoplasm will contract, 

 and rounding itself off, ultimately appear as a more or 

 less irregularly oval or spherical body. 



c. Mount a fresh specimen in water, and irrigate with 

 glycerine ; similar results will be seen to those already 

 observed on cells of the Apple : the cells will collapse, 

 owing to the sudden abstraction of water of the cell-sap. 



d. Mount a fresh preparation in water : irrigate with 

 potash solution, and observe that the protoplasmic con- 

 tents swell and lose their definite outline, and the 

 whole becomes more transparent. 



III. The above example of a simple Alga shows cells 

 aggregated in a linear series, constituting a filament : 

 the next specimen illustrates the more complicated 



