Correlation 



113 



to differential growth rates in various dimensions ( Fig. 5-8 ) . In the long, 

 narrow types, such as the "club" gourd, length increases faster than 

 width but at a constant relative rate, the value of k being approximately 

 1.2. In other races, such as the "bottle" gourds, width increases faster than 

 length, k being about 0.8. In the latter race, which has an upper sterile 

 lobe and a lower fertile one with a constricted isthmus between, the 

 ratios of the diameters of these to each other and to the polar diameter 

 of the ovary are specific, so that, as the fruit grows, not only the ratio of 

 length to width changes but the form of the organ as a whole undergoes 



lOOOt 



I to 



Width (mm) 



Fig. 5-8. Relative growth of length to width (plotted logarithmically) of developing 

 fruits of several types of cucurbits. ( From Sinnott. ) 



precise development (Fig. 5-9). An organic pattern results not from one 

 or a few correlations between dimensions but from a complex of such 

 correlations. In crosses between the two gourd types mentioned, the value 

 of k has been found to segregate after crossing and at least in one 

 case in a simple fashion, suggesting that this is what is under direct 

 gene control (p. 423). Evidently the form of the mature fruit in such 

 cases depends not only upon the relative rate of its dimensional growth 

 but upon the total growth attained, so that the problem of the inheri- 

 tance of form involves not only the genetic basis of relative growth but 

 also that of size. 



Dimensional relationships are not constant throughout the plant. Dif- 



