22 F R E D M. U B E R 



here it is necessary to avoid species or strains knowii to be highly 

 variable in their characteristics since this variability is probablj^ best 

 explained at present on the basis of easily mutating genes. 



With higher organisms it is much more difficult, if not impossible, 

 to secure a pure line. Much progress has been made in the case of 

 standard laboratory animals in that thej^ have been inbred over a few 

 hundred generations. Likewise some plant materials are rather well 

 known genetically. Even though vigor and disease resistance in these 

 hgihly inbred strains may be unfavorable, still their use is indicated 

 in numerous experiments where otherwise the detection and the inter- 

 pretation of the experimental effects might be jeopardized or com- 

 promised. 



To employ a single inbred strain to study an experimental effect is 

 not sufl&cient, however, if generalized conclusions are to be reached. 

 It is then necessary to use several inbred strains which span the type 

 of reaction or effect under investigation. This is analogous to the 

 situations, mentioned in the previous section, in which the use of 

 diverse biological materials are indicated. 



Several unique solutions of the genetic problem have been found 

 for higher plant and animal experimentation. One of these is the 

 widespread use of tissue cultures. Although the tissue culture method 

 was developed for its superior advantages with respect to environ- 

 mental control, the elimination of the genetic constitution factor is 

 clearly of great importance. Not only numerous types of animal 

 tissues can be cultured almost indefinitely, but also various plant 

 tissues. A second solution is available for those plants which may be 

 propagated by cuttings, tubers, grafting, and related methods. With- 

 out passing through a sexual cycle, they thus achieve a constancy in 

 their genetic constitution. The possibility of eventual changes is not 

 completely eliminated, however, since random mutations may occur 

 in somatic tissue. 



F. CONSIDER TIME A FACTOR 



Once upon a time, when research progressed at a much slower 

 pace, a scientist could attack a problem in a leisurely fashion without 

 being disturbed unduly by the thought that another investigator 

 might find the answer first. At a somewhat later date in the history of 

 science it was customary for individuals to stake out claims and 

 reserve to themselves for rather indefinite periods of time the privilege 

 of conducting investigations on certain limited aspects of a subject. 



