1067 
investigated, the factors which are present for the breadth of the 
petal are inhibited by another factor C, whilst again another factor 
B is able to counteract the inhibitory action of C; B is the inhibi- 
tory factor of the inhibitory factor C. 
Because moreover the factors 6 and C together cause the blue colour 
of the flower, there arise complicated relationships with regard to 
the interdependence between the breadth and the colour of the petal. 
There are various cases known of the existence of inhibiting factors, 
but so far as I know the existence of factors which are able to 
counteract the inhibitory action of inhibiting factors, has not hitherto 
been demonstrated. 
It is moreover evident from this paper that the different mutual 
crossings of some varieties may lead to varying conclusions. 
When only the crossing of the common blue flax with the narrow- 
petalled white was investigated, one would have come to the con- 
clusion, that in the common blue flax the breadth and the colour 
are caused by the same factor or factors, or that the factors for 
these characters are completely coupled in these varieties. 
Knowing only the observations on the crossing of the Egyptian 
flax with the common white, one would have concluded that the 
factors for the breadth and colour of the petal are completely inde- 
pendent of each other. 
From the crossing of the Egyptian with the narrow-petalled white 
flax, without a knowledge of the results of the other crossings, one 
would, on the other hand, be obliged to postulate an interrelation 
between the factors for broadness and colour certainly insusceptible 
of further definition, whilst the factors for broadness apparently 
present here an exception to the Mendelian law of segregation. 
From this it is seen that the phenomena are much more complicated 
than the two first-mentioned crossings by themselves give evidence of. 
But at the same time the investigation of the different crossings 
together has proved, that, when two characters in the crossing behave 
quite independently, the inference cannot be drawn without further 
proof that there will also be no interrelation whatever between the 
factors which cause these characters. 
_ The above clearly shows how relative our knowledge is. Views 
on the presence and action of factors obtained by an investi- 
gation of one single crossing, however simple and well founded 
they may be, are liable to modification when even only one of the 
forms investigated is crossed with a third form. Hence it is necessary 
to cross the same form with more than one partner in order to 
arrive step by step at the truth, 
Groningen. Botanical Laboratory. 
