336 CARL HALLQVIST 

oxydase in the cell sap no difficulty is met with in explaining the old 
age coloration through the entrance into the vacuole of a protoplasma- 
tic oxydase, which in co-operation with the vacuolar chromogen de- 
velops the colour. (Cp. the hypothesis formulated by Jones with re- 
gard to the coloration of white types, Jones 1913, ref. in ScHIEMANN 
1915). The following facts, however, should be noted. The shade of 
the old age coloration depends on the nature of the modifying factors 
present (B and V), as said before. WHELDALE regards the effect of 
the modifying factors as a continued oxidation of the products of the 
primary oxidation through specific enzymes. Such enzymes must 
therefore in this case have been present in the cell sap of a white 
plant with the constitution rBV, for instance. Thus these enzymes 
would not be able to compensate the enzyme of the fundamental R- 
factor; this should be attained, however, by a foreign enzyme (the 
R-factor is absent), which enters the vacuole a rather strange phe- 

nomenon. 
This hypothesis of the changes in the permeability of the vacuolar 
membrane agrees also with the interpretation of the nature of the 
white types given by ScHIEMann. This is based on the facts established 
by WırtsTÄTTEr that the anthocyan colours have a tendency to form 
colourless isomeres, and that certain substances have a power to check 
this isomerisation. The cell sap would then be assumed to contain 
anthocyan but of its colourless isomeric variety. A regeneration of 
the coloured isomere would be made possible through the successive 
changes in the chemical composition of the cell sap, provided that 
the above discussed changes in the permeability of the vacuolar mem- 
brane take place. 
The above hypothesis is mentioned only as an example. Several 
other circumstances with similar effect may be conceived of as factors 
in the colour development of the flower. Furthermore, the change 
in the composition of the cell sap may just as well be accomplished 
through the withdrawal of a substance. It appears probable, however, 
that the development of colour in the white types follows this course 
or a similar one. 
In the scheme proposed the F-factor has been assumed to have - 
a general effect. It has also been assumed that the occurrence of 
diluted forms of the colours, determined by the presence of the other 
factors, is due to the absence of this F-factor. Dilution of blue has 
been found in all crosses, where dilution forms have been found at all, 
and full coloured blue has always been found at the same time 
