134 Plant Tissue Culture 



ment of animal tissue likewise consists of hun- 

 dreds of cells which behave as individuals. "What 

 we observe in measuring such a colony is the inte- 

 grated behavior of many individuals in which 

 whatever variations exist in the behavior of any 

 one individual disappear in the final average for 

 the colony. It is not at all certain that the individ- 

 uals in such a colony have behaved alike. In fol- 

 lowing the behavior of a root culture, on the other 

 hand, one is dealing with a single branch behaving 

 as an individual, so that the full measure of vari- 

 ability is immediately evident. It is only by taking 

 the average of a large number of such individual 

 cultures that one can get a picture truly comparable 

 to that of the single fungus, bacterial or fibroblast 

 colony. Since it is patently impossible to deal 

 with even hundreds of cultures at a time in abso- 

 lutely uniform conditions of environment, the indi- 

 vidual variability comes into unavoidable promi- 

 nence. 



Part of this variability doubtless arises as a 

 result of slight and unrecognized differences in 

 the environmental conditions to which individual 

 flasks are subjected. Anyone who has studied, for 

 example, the differences in atmospheric humidity 

 in different parts of a single greenhouse bench 

 knows how difficult it is to maintain uniform con- 

 ditions even a few inches apart. Not all variables 



