Introduction 9 



tions. Through the decomposition of water, plants 

 also obtain material for the manufacture of or- 

 ganic matter. While the presence of the water is 

 essential for protoplasmic activity, its withdrawal 

 does not necessarily kill the protoplasm. In plants, 

 especially, certain structures like spores and seeds 

 may be deprived as completely as possible of all 

 traces of free water without at all injuring the 

 vitality of the protoplasm, which quickly resumes 

 its activity when the necessary water is supplied. 

 While it is true that the chemical composition of 

 all protoplasm is much the same, it is equally clear 

 that it cannot be absolutely identical for any two 

 organisms. The enormous complexity of its con- 

 stitution offers room for infinite variations in both 

 the composition and arrangement of the ultimate 

 protoplasmic units; and it is reasonable to suppose 

 that the inherent variability of all organisms is to 

 be traced back finally to these inevitable variations 

 in the protoplasm of which they are built up. 



The Cell. With few exceptions the protoplasm 

 is segregated in definite bodies or cells. In all but 

 the very low r est plants the protoplasmic body of the 

 cell the " protoplast " always contains a well- 

 organized nucleus like that found in the cells of 

 animals. There are also in all of the green cells 

 definite bodies, chromatophores, in which is con- 

 tained the chlorophyll. Both the nucleus and 

 chromatophores always arise by division and are 

 never formed anew in the protoplasm. Other 



