PROTOPLASM 113 



struction and efficiency as compared with microscopes of today, 

 was beginning to be employed by Robert Hooke (1635-1703) 

 and others in the seventeenth century in the study of plants. 

 Robert Hooke, one of the earliest to study plants with the 

 microscope, examined thin sections of cork, and found the cork 

 to be composed of numerous small compartments which he 

 called cells on account of their rough resemblance to the cells 

 of a honeycomb. Of course in dead tissue like cork the cell 

 contents are absent, and Robert Hooke saw only the cell walls 

 enclosing the spaces from which the active substance of the 

 cells had departed. However, through investigations which fol- 

 lowed those of these earliest investigators with the microscope, 

 it gradually came to be recognized that the important part of 

 the cell is the substance which fills the compartments. By ex- 

 tending the study to many kinds of tissues of both plants and 

 animals, it was finally recognized that the substance filling the 

 cell is the only living substance in plants and animals and the 

 substance which builds the cell wall and the entire organism. 

 Various names were at first applied to this substance before the 

 term protoplasm suggested by Hugo Von Mohl was adopted by 

 both botanists and zoologists. As the word protoplasm, which 

 is a combination of protos (first) and plasma (thing formed), sig- 

 nifies, this substance was considered the first organic substance 

 formed from the inorganic materials taken into the plant. The 

 idea that the protoplasm is the essential substance and that the 

 cell is the unit of plant and animal structure was quite thoroughly 

 elaborated by Schleiden (1838) and Schwann (1839) and became 

 generally accepted. 



Protoplasm. — The protoplasm, as already noted, is the living 

 substance of plants and animals. The protoplasm of an indi- 

 vidual cell is often called a protoplast. Protoplasm is a fluid 

 substance which varies much in its consistency, sometimes being 

 a thin viscous fluid like the white of an egg, and sometimes being 

 more dense and compactly organized. Chemical analyses show 

 that protoplasm has the composition of protein, although such 

 analyses necessarily kill the protoplasm and consequently do not 

 give us a true knowledge of the protoplasm as it is while living. 

 Although the protoplasm of higher plants usually exhibits no 

 motion except when dividing, there are cases, however, as in the 

 hairs of the Pumpkin and Wandering Jew, where the protoplasm, 



