232 
like some bears and the chamois. Probably tliere are a great 
number of animals in which the difFerence between the tempera- 
ture-coefficients of feather (hair) growth and that of pigment- 
formation would be considerable enough to cause such a seasonal 
dimorphism, if only they lived in a countiy where the temperature 
at the time of their springmoult differed sufficiently from that 
at the time of the autumnmoult. Further, it Stands to reason 
that animals which only moult once a year can never show 
seasonal dimorphism from this cause. Such may be the case of 
the gyrfalcon, which is constantly light in northern countries, 
and coloured at other places. 
In all organisms that have been studied in respect to both 
genetic and non-genetic factors in their development the inter- 
relation of these two groups has been very obvious. In making 
the best possible economic use of an organism, it always pays to 
study this interrelation, and to find in how far it will be possible 
or profitable to change some or more of these factors. 
There are always tAvo ways of making the cultivation of 
an animal or plant pay better than it does, either one can change 
the set of genetic factors to suit the existing non-genetic ones, 
or eise, one can change these latter to suit an existing biotype. 
The study of the suitable non-genetic factors in the pro- 
duction of animals and plants is the subject of constant study 
at the agricultural and horticultural experimentstations. Th 
manipulation of the genetic factors has until recently consisted 
entirely in a more or less conscious selection. The research-work 
with genetic factors of the last ten years has given us a basis 
upon which the experimental breeder can build forth, to improve 
the genetic Constitution of the cultivated animals and plants. We 
can make the animal or plant to suit the conditions and methods 
of cultivation only in as far as we have the required genetic 
factors to combine or, if the elimination of some factor or factors 
is required, if we can find at least one individual devoid of 
them. In very many cases, as in agricultural plants where 
methods of cultivation can not vary very much, or where as in 
the case of climate, it is impossible to change one important 
non-genetic factor, we simple have to produce a biotype which 
will develop in a satisfactory way even with such non-genetic 
factors as we have. In other cases, it will be found impossible 
to change the genetic Constitution of an organism. For instance 
