io6 



THE PLANT CELL 



be empty, but which is filled with a watery liquid termed 

 cell-sap. 



(i) The cell-wall is formed of a solid, elastic and transparent 

 dead material, called cellulose by chemists ; it acts as a protective 

 covering for the protoplasm and is manufactured by the latter. 



(ii) The protoplasm, which is the most important part of the 

 cell, is a more or less slimy or jelly-like substance containing 



n 



Fig. 49. — -.4, Very young cell from near the tip of a root. B^ Two older 

 cells. C, Single full-grown cell; a cell-wall; r cytoplasm : « nucleus ; ^ 

 plastids; v vacuole. (Enlarged about 350 diameters.) 



a considerable proportion of water. Its chemical nature is not 

 understood, but within it there always appears to be a complex 

 mixture of protein compounds. It is the substance directly 

 associated with the peculiar phenomena which we call life. 

 The process of respiration, and all the remarkable chemical 

 changes involved in ' assimilation ' and nutrition generally, are 

 due to the protoplasm, as well as the powers of growth and 

 reproduction possessed by living organisms of all kinds, plants 

 and animals alike. Wherever life is, protoplasm is present, and 

 death implies its decomposition or destruction. 



