98 SIRKS, THE COLOURFACTORS OF THE SEEDCOAT IN PHASEOLUS 
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or less probability, and moreover in many cases it is perfectly 
immaterial in these researches that the fatherplant is unknown. 
For all crosses, made with a white-seeded plant as one of the 
parents, have the same shortcoming because of the uncertainty in 
its genotypic constitution of this white plant; one and the same 
white race of beans may contain plants very different in factorial 
constitution with regard to the seedcoat-characters; as now 
known a white-seeded plant is white because of lacking a 
certain groundfactor, but it may contain a great many other factors, 
that remain unvisible because of the absence of the groundfactor. 
Thus spontaneous hybridization may offer to us a very welcome 
subsidiary material for researches; their analysis has been applied 
by Kasanus (1914), LUNDBERG and AAKERMAN (1917), TyEBBEs and 
KOOIMAN (1919), Sırks (1920). Such an analysis is only complete, 
if all seeds from an F;-plant, that originated by spontaneous 
hybridization, are available and accordingly the whole Fo- and 
following generations can be grown; only the papers of LUNDBERG 
and AAKERMAN and my own have been worked out in this manner; 
KAJANUS as also TJEBBES and KOOIMAN have derived their materials 
from only one seed with a seedcoat divergent from those of the race of 
origin. Of course this seed had been developed upon an F;-plant, and 
the embryo contained init, was thus an Fo-individual. This does not 
necessarily involve an essential fault, so less as the little number of 
Fo-individuals gives in simple cases only a sufficient result, but 
notwithstanding a danger remains and an important difficulty may 
not be disregarded. The posterity of this seed, grown as F:- 
generation, may be wholly uniform, and in that case its importance 
for a genotypic analysis of the parents fails, and secondly this Fo- 
individual will in most cases possess only a part of the whole num- 
ber of genetic factors, that was present in the F;-plant and so 
in the Fo-generation. It will be even conceivable, that the Fo-plant 
grown, lacks all seedcoatfactors present in the known motherplant, 
and the analysis of its F3-generation will be therefore very decei- 
ving. In many cases growing the whole Fo-generation is necessary, 
and growing the whole number of F3-families obtained very much 
desired for founding sound conclusions. 
In this paper a review will be given of the results obtained by 
previous authors and of the genetic factors for the seedcoatcolours 
