12 Plant Tissue Culture 



intellect. As regards living organisms, this prob- 

 lem embraces everything that we include under 

 the name of "morphogenesis." Since the cell is 

 theoretically the ultimate unit of structure in liv- 

 ing organisms, the question of the origin of form 

 and function in living beings may be stated thus : 

 "Are the factors which determine these charac- 

 teristics external to the individual cell (in which 

 case the cell is totipotent but its particular expres- 

 sion comes about through a potentially reversible 

 suppression of some of its potencies due to its 

 spatial association with other cells), or are they 

 internal, in the individual cell (in which case the 

 cell is obviously not totipotent but has lost some 

 of its potencies at some point in the sequence of 

 events which constitute its temporal association 

 with other cells)?" One method of deciding be- 

 tween these two possibilities lies in the isolation 

 and cultivation of individual cells as separate 

 units or elementary organisms. The technique 

 of isolating and studying cells in this way has, in 

 the last four decades, become established as the 

 technique of "tissue culture." 



