ALBERT C. HILDEBRANDT 



401 



were most frequently scattered among the hyperplastic regions and often 

 were not orientated in the same direction as those of adjacent tracheal 

 elements. This suggested a lack of organization. 



Tissues grown at weak concentrations had larger hypertrophic cells 

 than control pieces. The total number of cells per unit area was less, 

 and there were many more scalariform vessels. To determine this rela- 

 tionship actual counts were made of the number of cells in fifty fields 



TABLE 2 



Comparison of the Number of Meristematic Cells and of Tracheal Elements 



of Sunflower Tissue of Crown-Gall Origin Grown on Media Containing Weak 



or Strong Concentrations of Growth-Regulating Substance and on Control 



Media Lacking Added Growth-Regulating Substance 



Growth-regulating 



substance and 



cell type 



Cells in 50 fields of sections of tissue 



cultured with indicated concentrations 



of growth-regulating substance* 



Strong Weak None L.S.D.f 



Indole-3-acetic acid 

 Meristematic cells 

 Tracheal elements 



Indolebutyric acid 

 Meristematic cells 

 Tracheal elements 



a-naphthaleneacetic acid 

 Meristematic cells 

 Tracheal elements 



/7-chlorophenoxyacetic acid 

 Meristematic cells 

 Tracheal elements 



No. 



No. 



No. 



*Concen(xations indicated in text. fNumber of cells required between treat- 

 ment totals for significance at the 5 per cent level. 



each about 1/4 sq. mm. in size in cultures incubated on weak or strong 

 concentrations of the four growth-regulating substances and on the 

 control media. The total numbers of cells in the tissue sections examined 

 from these media are summarized in Table 2. These counts indicated 

 that the weaker concentrations stimulated greater cell size and a greater 

 proportion of scalariform vessels. 



Strong concentrations of growth-regulating substances resulted in a 

 striking decrease in wet weight as compared with controls (Fig. i). 



