NATURE AND POWERS OF PROTOPLAST 1 7 



The Chemical and Physical Nature and Physiological 

 Powers of the Protoplast.— The exact chemical constitution 

 of the protoplast is not known. The evidence thus far at hand 

 goes to show that it is chiefly a complex of proteids of very large 

 molecules where the elements carbon, hydrogen, oxygen, and 

 nitrogen are always present, and frequently sulphur, and, in the 

 nucleus, phosphorus. Water is always associated with the pro- 

 toplast and is necessary to its life. Other substances than the 

 proteids and water are sometimes, and may be always, present. 

 On account of its complex nature the plasma or substance of the 

 protoplast is easily broken down into simpler substances, setting 

 free large amounts of energy; and correspondingly large amounts 

 are required for its growth and repair. 



In consistency the protoplast is apparently semi-fluid. We get 

 this conception from the rotation and circulation of the cytoplasm 

 in Nitella, stamen hairs of Tradescantia, Myxomycete plasmodia, 

 etc. Here the cytoplasm simulates a fluid in its streaming move- 

 ments, while it preserves its form sharply demarked from the 

 surrounding cell-sap. The Plasmodium of Myxomycetes con- 

 sists of a mass of cytoplasm with many embedded nuclei, and no 

 cell- walls are present; so that its consistency, which is about that 

 of thin batter, may be taken as aia indication of the consistency 

 of protoplasts in general. The nucleus and plastids seem to be 

 firmer and less fluid than the general cytoplasm, but their mobility 

 is shown by the apparent ease with which they change their form; 

 as when chloroplasts round themselves up or flatten out with 

 varying intensities of light, and nuclei of tapetal cells flatten them- 

 selves and creep into very narrow rifts between groups of 

 developing spores (Fig. 9). 



. The things which the protoplast is capable of doing as a physio- 

 logical unit have partly been told in the foregoing, and will be 

 further brought out in succeeding chapters. By way of con- 

 venient oversight these activities will now be grouped and 

 classified : 



{a) Absorption. — Water, and solids and gases in solution, are 

 drawn through the plasnia membranes into the meshes of the 



