102 sIRKS, THE COLOURFACTORS OF THE SEEDCOAT IN PHASEOLUS 
other uniformly coloured races, Fj-generations with marbled seeds 
and segregating in Fo into 1 marbled:1 selfcoloured (for example 
237 m: 239 s). | 
In addition to this Kooıman (1920, p. 36 ff.) reports to have found 
that not all Fs-families, descended from marbled F,-plants, show 
this 1:1-proportion. His Fo-family segregated into 75 marbled: 71 
self coloured individuals, but among the Fg-cultures a great many 
splitted up according to 2:1 (46 marbled: 26 uniformly coloured), 
so that 662/3 of the total had marbled seedcoats, while in other 
Fs-families the percentage of marbled individuals was 53.30/ç, in 
still others 50 90. 
The discussions of this phenomenon have gone through a great many 
changes. At the beginning both types of marbling: the constant and 
the eversporting form were sharply separated; the firstmentioned 
type was caused in TSCHERMAKS opinion by only one dominant 
mendelian factor; the other was an eversporting character, called 
up from a state of latency, in which it was present in the uniformly 
coloured race. Afterwards (1908) SHULL has supposed this latent 
character as being present in the white parent, and this factor M 
would be observable in heterozygotic condition only; M M as 
also m m-individuals are therefore uniformly coloured, M m- 
individuals are marbled. ~Constant marbling was in his opinion 
caused by a separate dominant factor. EMERSON had at first accepted 
this hypothesis as proposed by SHULL, but in a later paper (1909 b) 
he has changed his opinion and preferred another hypothesis, the 
proposal of which had been made by SPiLLMAN. This author thinks, 
that races with constant marbling may possess two factors in ab- 
solute linkage, that would remain always together in the gametes; 
being separated from each other these factors would be invisible. 
Thus three forms of selfcoloured beans could exist: one with 
one of these marbling factors, but lacking the other; a second 
type possessing the other, but missing the first one and as third 
ease a bean, in which both factors fail. If we call with EMERSON 
these factors Y and Z, so in collaboration with the pigmentation- 
factor P four types of coloured and four types of white beans 
may exist, viz.: 4 
1 P Y Z = marbled. 
2 P Y z = selfcoloured, with one latent marbling factor. 
