ASPECTS OF KINETIC EVOLUTION 263 



and accentuate conditions of degeneration. Many varieties of 

 domesticated plants and animals have been bred so long and so 

 narrowly in one particular locality that any change is accom- 

 panied by notable deterioration. Thus it comes to be believed 

 that seeds of one particular plant, such as the radish or the 

 cauliflower, can be grown to perfection only at Erfurt. Trans- 

 ferred to any other point, neotopic mutation at once appears and 

 brings diversity and commercial inferiority. In a similar way 

 many high-bred animals like the Jersey cattle also deteriorate 

 or show special susceptibility to disease when subjected to new 

 conditions, even to those in which other less closely adjusted 

 breeds are able to thrive. 



BEARING OF NEOTOPISM UPON ACCLIMATIZATION. 



Neotopism must also be taken into account in another depart- 

 ment of agricultural investigation. The phenomenon is often 

 very marked in plants introduced from tropical countries into tem- 

 perate regions, and has had the opposite effect of deceiving 

 us regarding the possibility of acclimatizing species or varieties 

 of tropical origin. The popular impression is that the colder 

 climate of our more northern latitudes will restrict the growth 

 of plants from the tropics, but this is the reverse of what usually 

 happens, as a matter of fact. It seems to be a general law that 

 annual-crop plants, whether of temperate or of tropical origin, are 

 most vigorous and productive near their northern limit of growth. 

 The reason for this is that the longer days supply a greater 

 amount of heat and sunlight than in the tropics themselves. 



Plants newly introduced from the tropics commonly misuse 

 these exceptionally favorable conditions to put forth an abnor- 

 mal amount of vegetative growth and are often killed by frost 

 before they commence fruiting. It has been usual to explain 

 the failure of such experiments on the simple ground that our 

 northern season has proved too short for these tropical varieties, 

 but as a matter of fact the time may have been equal to that 

 required by these same varieties for normal growth and maturity 

 at home in the tropics. Thus the Kekchi variety of Upland 

 cotton, which matures seeds in Eastern Guatemala in five months 

 from planting, required in Texas over six months to produce 



Proc. Wash. Acad. Sci., January, 1907. 



