FUNDAMENTAL INTERNAL STRUCTURE OF PLANT BODY 5 



that the separate units making up the cork tissue resemble 

 the cells of a honeycomb, and hence Hooke gave the name 

 " cell " to the units of cork tissue. Although an inappropriate 

 name, in that the majority of plant cells have no resemblance 

 to those of a honeycomb, the name still clings to botanical 

 terminology. Hooke's discovery, although an epoch in the 

 history of biology, was to be followed by others of far greater 

 importance in that they tell us of the real nature of the cell, 

 its marvelous inner structure, and most wonderful activities. 



The Cell as a Unit of Structure. — Just as a brick house is 

 made up of individual units, the bricks, so is a plant composed 

 of individual units, the cells. A plant is made up of cells and 

 the products of cells, and nothing else. The wood, the root, 

 the flower parts, the leaf, are made up of cells and cell prod- 

 ucts. This must not be understood to mean that all parts 

 of a plant are alive; but the non-Hving portions are products 

 of the living material within the cell. 



The Cell as a Unit of Plant Activity. — The activities of a 

 plant take place within the cells, for it is within them that 

 we find the living material— protoplasm. Some of the sim- 

 plest plants are unicellular, that is, one-celled. In such a 

 case, the individual plant is simply one cell. That one cell, 

 that individual, is capable of carrying on all the processes — 

 absorption, respiration, digestion, assimilation, reproduction, 

 etc. — upon which its life and the life of the race to which 

 that plant belongs are dependent. Somewhat higher in the 

 scale of plant life, we find some plants, algae, for example, 

 composed of a number of cells, several hundred, for instance. 

 In this case, the individual plant is multicellular, and yet, in 

 this plant, each cell is a unit of activity, and each carries on 

 its activities quite independently of the others to which it is 

 united, as is evidenced by the ability of the individual cells 

 to Uve and reproduce when separated from its neighbors. In 



