264 THE AMEHICAN MONTHLY [Aug. 



manent mount can be made with glycerine jelly, the latter 

 is melted and then applied in the same way as glycerine. 

 All preserved specimens should be labeled so as to re- 

 cord their history as fully as possible. 



4. Epidermis of the Onion is an easy object on which 

 to demonstrate protoplasm in the cell. Protoplasm is 

 a semi-fluid finely-granular material contained inall living 

 cells; the practical biologist must learn as early as possible 

 to recognize it, and distinguish it from the other cell con- 

 tents if there are any. To seeitjtakeanonionand carefully 

 remove a small bit of the skin on the glistening surface 

 of one of the inner leaves and mount it in water. In 

 contrast with the potato the onion is a very short stem 

 whose leaves are close together and modified for the 

 storage of starch. Care must be taken to get only the 

 outer layer of skin. Study the piece and note the forms of 

 the cells, select one for careful study and carefully lo- 

 cate the granular matter, protoplasm, on its surface; and 

 the round granular nucleus; note also the thickness of its 

 wall; does the centre of the cell contain protoplasm ? 

 Remove the cover glass and stain well with iodine, wash 

 out and cover and then re-examine, the protoplasm and 

 nucleus onght, if successful, to be stained; do you find any 

 evidence of the presence of starch ? Make another mount 

 and in this case apply 10 per cent nitric acid to the cells, 

 wash, cover and examine and you will see that now the 

 centre of the cell is occupied with granular material and 

 the surface is clear, the water that before occupied the 

 centre has been drawn out and the protoplasm has 

 shrunken away from the wall into the centre of the 

 cell. Record this and all your observations by careful 

 drawings, in which each cell is accurately represented, 

 and fully index. 



5. Mammalian Liver.* — We have now seen that plants 



*If sections of the liver are not available, other animal tissues will serve. 



