THE WALLFLOWER 29 



ever, the cell-walls are still very thin, and for this 

 reason growing -points are very delicate, and require 

 external protection, which in. the case of stems is 

 afforded by the surrounding leaves. 



The interior of the cell is almost completely filled by 

 a soft, viscid, finely granular substance, the protoplasm. 

 The outer part of the protoplasm, where it borders on 

 the cell-wall, is clearer that is, more free from granules 

 than the rest. The protoplasm consists of a mixture 

 of various substances, called by chemists proteids, which 

 are more or less similar in composition to albumen 

 or white of egg. These are very complicated bodies, 

 about which little is known chemically ; they are com- 

 posed of the five elements, carbon, hydrogen, oxygen, 

 nitrogen, and sulphur. Besides the proteids, active 

 protoplasm always contains a large proportion of 

 water. Physically it resembles a very thick fluid, but 

 it has powers of spontaneous movement and continuous 

 changes of form such as no fluid possesses. 1 Proto- 

 plasm is found in all cells without exception in which 

 growth is going on, or in which food is assimilated, or 

 any new structure formed, or any kind of spontaneous 

 movement carried out. It is, in fact, the seat of all 

 those processes (whether in plants or animals) which 

 distinguish living organisms from lifeless matter. The 

 word " protoplasm," meaning that which is first formed, 

 was invented by the Bohemian physiologist Purkinje 

 in 1840, and was used independently by the German 

 botanist von Mohl in 1846, to express the fact that 



1 No part of the Wallflower plant is convenient for observing these 

 movements of protoplasm, so some special illustrations of them from 

 other plants will be given below (see p. 41). 



