232 



like some bears and the chamois. Probably there 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 country 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 two 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 else ; 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. The 

 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 



