4l6 THE HEREDITARY FACTORS AND DIFFERENTIATION 



are here concerned are, first, the total amount of material in the 

 organ (which itself is likely to be related to the total bulk of the 

 organism by a non-linear formula), and, secondly, the relative in- 

 tensity of growth in the different planes of space within this mass 

 of material. The fundamental processes are concerned with the 

 ratios of the linear dimensions, not with the linear dimensions 



« (^ 



B n f) 



w f) 



Fig. 199 

 Shape-genes in gourds {Cucurbitd). Five stages in the development of ovary and 

 fruit in A, elongate ; B, spherical ; and C, disc types ; showing progressive change 

 of shape of the fruit-rudiment. (From Sinnott and Durham, Bot. Gaz. Lxxxvii, 

 1929.) 



separately. This concept has been applied to the analysis of the size 

 and shape of gourd fruits,^ where it is found that a genetic analysis 

 on the basis of linear dimensions leads to confused results, whereas 

 an analysis on the basis of ratios between length and breadth 

 permits of a simple interpretation of the results in terms of a few 

 clearly defined ** shape-genes" (figs. 199, 200). 



^ Sinnott and Hammond, 1930. 



