THE ORIGIN OF THE PLANT TUMOR CELL 



615 



metabolism characteristic of di£Ferentiated cells of higher organisms, 

 again predominates as a result of the cellular transformation. 



The question as to whether this new pattern of synthesis found in 

 the tumor cell results in an irreversible loss of the previous pattern con- 

 cerned with diflFerentiated function, or whether it simply overwhelms 

 the latter, has been investigated in the crown-gall disease (Braun, 

 1951b, 1959). There are produced in plants, in addition to the per- 

 manently altered tumor cells of the unorganized type, complex tumors, 

 or teratomata, composed of a chaotic assembly of tissues and organs 

 which show varying degrees of morphological development. Terato- 

 mata arise when pluripotent cells, which possess highly developed re- 

 generative capacities at the time of their alteration, are transformed to 

 tumor cells. The use of clones of teratoma tissue of single-cell origin 

 has permitted the unequivocal demonstration that the complex tumors 



Figure 1. A. Culture of crown-gall tobacco tumor tissue of the unorganized type. B. Re- 

 sult obtained when a fragment of sterile tumor tissue of the type shown in A was grafted 

 to the cut stem end of a tobacco plant. C. Culture of crown-gall tobacco teratoma 

 tissue. D. Result obtained when a fragment of sterile teratoma tissue was grafted to the 

 cut stem end of a tobacco plant. 



