FLOWER AND SEED COLOUR IN LUPINUS 339 



colour is weakened. The full colour factor, then, is not pleiotropic 
to the same degree as the colour factors. 
Another interesting point of some weight has been mentioned 
with regard to the pleiotropism of the colour factors, which illustrates 
the common phenomenon that the effect of a pleiotropic factor differs 
in different organs. Two different cases of pleiotropism may be found. 
In the first case the factor has the same effect in different .organs; 
blue colour in the flower as well as in vegetative parts as in Lupinus, 
and zygomorphism in both calyx and corolla as in Antirrhinum, accor- 
ding to Baur, are good examples of this first kind. In the second 
case the effect of the factor varies in different degrees in different 
organs. Many examples are known of this kind, as for instance blue 
flower colour and earth-brown seed colour (Lupinus), and the flower 
colour and the width of the petals (Tammes in Linum) to mention 
a more surprising case. The terms isophene and heterophene 
pleiotropism are proposed for these two kinds of pleiotropism. The iso- 
phene pleiotropism is clear enough but the heterophene kind present 
sometimes very unexpected combinations. However, the above men- 
tioned case of heterophene pleiotropism in Lupinus (blue flower colour 
and earth-brown seed colour) is as readily explained as the isophene 
pleiotropism. When the immature seed is examined it is seen, as said 
before, that the earth-brown coloration induced by the factor B, really 
is a blue coloration, which passes into the earth-brown colour in con- 
sequence of maturing processes. In this case a morphological obser- 
vation suffices to show that the means of action of the pleiotropic 
factor are the same in the both organs; the cause of the different 
phenotypical effects of the factor is wholly due to different conditions 
prevailing in the both organs. Another illustrative example of this 
kind of pleiotropism is the interpretation given by HERIBERT-NILSSON 
to account for the cracked bark and the curved leaves of certain 
segregates of Salix-bastards; both these characters are traced back 
to an abnormal rate of growth of the vascular cylinder (the xylem). 
A careful anatomical, physiological or chemical analysis of marked 
heterophene pleiotropism shall probably in many cases similarly bring 
out the fact that the differences are to be traced back to a common 
cause. The phenotypical diversity, of course, is due to one and the 
same undifferentiated genetical factor in these cases. As long as 
the real nature of the factors is unknown, there is no use of discussing 
the question, whether the genetical factor should be assumed to be 
undifferentiated and simple in the case of characters showing gene- 
