358 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 40 



Incidentally, this statement by a botanist antedates by some years 

 the first work with animal-tissue cultures, which in the hands of 

 Carrel and others, has yielded such noteworthy results. 



Any definition of just what constitutes a tissue culture must be 

 arbitrary. For the present it may be convenient to adopt the defini- 

 tion formulted by White, who considers a plant-tissue culture to be 

 "any preparation of one or more isolated, somatic plant cells which 

 grows and functions normally, in vitro, without giving rise to an en- 

 tire plant." This would exclude spore cultures, cultures of whole 

 embroys, or other propagula. It should be realized, however, that 

 this definition contains a joker, namely, the requirement of "normal" 

 growth and function; to determine whether growth and function of a 

 culture are indeed normal may at times be a task of almost insur- 

 mountable difficulty. 



Although it was early realized that tissue cultures might furnish 

 a very useful tool in the elucidation of many problems, it was not 

 foreseen how laborious would be the fashioning and sharpening of 

 the tool for use. This preliminary technical preparation, which has 

 been attended by many difficulties, has been the objective of most of 

 the work so far accomplished and it is only in the last few years 

 that the ground work has been developed sufficiently for the appli- 

 cation of the method to other problems. 



It is of interest to review briefly some of the highlights of the work 

 of the past four decades. 



Although a considerable amount of work was done by Haberlandt 

 and his students and by other investigators, the early results were 

 not encouraging. The immediate impetus for recent work has come 

 from the successful cultivation of excised roots, and the present 

 account will be concerned principally with this phase. 



By one of those coincidences that sometimes occur in experimental 

 work two investigators, Kotte in Germany and Robbins in the United 

 States, without knowledge of each other's work, published in 1922 the 

 first reports on cultivation of excised root tips in nutrient media. 

 Curiously enough, both investigated the roots of peas and corn. The 

 general teclinique adopted in these experiments and in nearly all 

 subsequent studies was to cut off the root tip of a seedling which 

 had germinated under aseptic conditions, transfer it to the nutrient 

 medium, allow it to grow for a week or two, again cut off the tip 

 and transfer this to fresh media. This procedure was continued as 

 long as growth ensued, the objective being to prepare an environment 

 in which growth would proceed indefinitely. Such continued growth 

 was not achieved by either Kotte or Robbins, and success was first 

 attained a decade later by White with tomato roots. Using a liquid 

 medium containing sugar, a number of inorganic ions, and a small 

 amount of a water extract of yeast, White has been able to maintain 



