THE HISTOLOGY OF THE .CELL 79 



acid. A lignified wall is stained brown and swells, and a corky wall is 

 stained brown but does not swell. 



EXPT. 75. Soak some Linseed seeds in water, and note how they 

 swell. The outer layers of the seed, which were hard and horny, have 

 been converted into mucilage. 



Make a section from a dry seed and mount in glycerine and water. 

 Examine with a low power, and notice the wall swells and the 

 striations on it become very clear. 



The Protoplasm. The protoplasm is the living and active 

 part of the cell. It is a semi -solid material, which has embedded 

 in it a number of granules, and is kept moist by the cell-sap, 

 which saturates the wnole of the cell. 



It is probable that the protoplasm consists of a number of 

 fibres which cross in all directions to form a net-work, the 

 meshes of which are filled in with a more fluid substance. 



In living cells the protoplasm is always in close contact with 

 the cell-wall ; but if the temperature of the cells be raised to 

 120 F, the protoplasm coagulates, i.e., sets like the white of an 

 egg when boiled. In this state it loses all power of movement 

 and dies. Alcohol or weak acids produce similar result. 



The Composition of Protoplasm. If a few cells are 

 treated with iodine, the protoplasm is coloured brown. This 

 is the same colour which the substances called proteids give with 

 iodine, and it seems very probable that protoplasm is built up of 

 proteids. 



A proteid is a substance which contains Carbon. Hydrogen, Oxygen, 

 Nitrogen, and Sulphur. The essential element of a proteid is nitrogen, 

 and in some cases the name nitrogenous substance is used in place of 

 proteid. The proportion of the above elements in living protoplasm 

 is not known. If an analysis is made of protoplasm it is necessary to 

 kill it in the process, and there may be a difference between the com- 

 position of living and dead protoplasm. Protoplasm certainly contains 

 the same elements which are found in proteids. It is the most wonder- 

 ful substance in the universe, because life is never found apart from it. 

 There appears to be no difference between the protoplasm of plants and 

 that of animals. 



The Movement of Protoplasm. The protoplasm of a 

 plant cell possesses the power of movement. These movements 

 can be observed in large cells with thin and transparent walls, 

 especially when the colourless protoplasm contains a large 

 number of granules. These granules are driven backwards and 

 forwards with the stream, and they appear much as particles of 



