26 PKACTICAL BOTANY 



protoplasm (" primordial utricle " of the older 

 botanists). 



4. A large internal cavity bounded by the protoplasm : 

 this is the vacuole, or cell-cavity. 



The distinction between the parts of the cell may be 

 brought out more clearly by means of the following 

 reagents : 



a. Irrigate (p. 15) continuously for some minutes 

 with a 2^ per cent, solution of common salt (that is, the 

 5 per cent, solution diluted to double its volume) : the 

 cell-wall will retain its original position and appearance, 

 but the film of protoplasm will be seen to contract and 

 gradually to separate from the cell- wall ; the separation 

 usually extends over only a part of the surface, but it 

 is sufficient to allow the cell-wall and protoplasm to be 

 easily distinguished. 



I. Treat a freshly prepared specimen with iodine 

 solution: the cell-wall is not appreciably stained, but 

 the protoplasm stains a more or less deep brown. A 

 small oval body, which stains a deeper brown than the 

 rest of the protoplasm, may often be seen included in 

 it : this is the nucleus. 



c. Treat another fresh specimen with glycerine, and 

 watch the eifect : many of the cells will lose their oval 

 form, and collapse, the cell-wall being thrown into 

 irregular folds. From this it will be at once seen that if 

 specimens of a fresh tissue be placed directly in glycerine 

 the cells are liable to change of form, which is owing to 

 the sudden extraction of water from them : care should 

 therefore be taken in the treatment of fresh material 

 with glycerine, otherwise good specimens may be 

 readily spoiled. 



