FACTORS AFFECTING SEASONAL ACTIVITIES. n 



dinal points, including the optiuinui for growth and develop- 

 ment, may be altered by other conditions which affect the plant. 

 The variation of which a plant is capable represents its possible 

 geographical range which may be mapped with fair accuracy. 

 Thus the individuals of a species which live nearest the pole have 

 made such accommodations that they are able to accomplish de- 

 velopment with a minimum number of heat units, in a minimum 

 number of hours. As the range of a species is traversed toward 

 the equator or to lower elevations, a place is reached where the 

 heat exposures are at an optimum for the plant, and beyond this, 

 development is retarded until the southern limit of the species is 

 reached. The actual limits are of course determined by the en- 

 tire complex of conditions, of which insolation is also an im- 

 portant factor, but for the sake of clearness, attention is focussed 

 upon temperature alone. 



The gradual accommodation and acclimatization of grains 

 to regions to the northward has nowhere been more systematic- 

 ally studied than in the Scandinavian peninsula, and Schubeler's 

 consideration of available results led to the conclusion that corn 

 from lower latitudes or elevations ripened earlier when taken 

 northward and upward, although the light and average tempera- 

 ture was less. This precocity in development persisted for some 

 time, when seeds were taken back to the southern localities. In 

 some cases the seeds and sometimes the leaves reached a greater 

 size if the conditions permitted full development in the northern 

 extensions, but this accommodation was not carried to the first 

 generation in plants in the south from northern grown seeds. It 

 was also noted that the colors of various organs as well as the 

 aroma w^as increased in plants taken northward if the introduc- 

 tion did not go beyond the limit of conditions allowing full de- 

 velopment. (Schubeler, F. C. Viridarum Norvegicum. Norges 

 Vaxtrage. Et Bidrag til Nord-Europas Natur-Og Kulturhis- 

 torie. I. Christiania, 1885. Rev. in Bot. centralb. 28: 203. 1886.) 



The relation of the plant to negative exposures is one of en- 

 durance and not of performance, and the interpretation of the 

 influence of cold upon distribution may not be made by the for- 

 mula given above. The total amount of negative or cold ex- 

 posure is undoubtedly the predominating one, but the minimum. 



