270 



KAHL B. KRISTOFFERSON 



lent ()l)ject for the study of (jiiantitative characters. Irrej,'iilarities due 

 hi the seasonal modification are as easy to avoid — for instance hy 

 making all measurements during the same season — as the modifi- 

 cations due to differences in the soil are difficult to avoid. However, 

 Viola has other characters that are rather unpleasant. The germina- 

 tion of the seeds is very capricious, a fact to wliich 1 often have called 

 attention. I'^urther, V. tricolor is herkogamous, as Nvell as Fi and i)art 

 of /'\. of the crosses with this species, and therefore it is necessary to 

 pollinate artificially. The sudden bursting of the capsules is another 

 unpleasant character. It may be rather difficult to follow the ripening 

 of the capsules. This is especially the case in warm and dry weather. 



I have made use of the length of the petals as a standard of the 

 size of the corolla. The breadth varies, at least in some degree, in- 

 dependent of the length, but I had no time to measure this character. 

 By the measurements I have made use of an apparatus similar to 

 that used by Johannsen (1913) in his work on beans. The scale and 

 figures were engraved on a thick plate of glass in such a manner that it 

 was possible to lay the scale directly upon the petals. The length of the 

 long sides of the triangle w^as 10 times longer than the short one and 

 therefore the length of the petals was easy to read off. With this 

 apparatus it was possible to measure with a correctness of 

 about 0,1 mm. 



In order to determine the means of the length of the petals I have 

 measured 20 — 30 plants of the parent-lines and Fi. All fully developed 

 flowers were measured on each plant. The measurements are put 

 together in table 9. 



TABLE 9. The length of the petals in the parent-lines and Fa. 



The lines 10 and 40 belong to V. tricolor, and the lines 2, 3 and 

 25 to V. arvensis. 



As is to be seen in table 9 the dominant influence of the small- 

 flowering forms of V. aruensis is very striking. The bastards between 



