226 THE PLANT WORLD, 



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 Scandianvian peninsula, and Schubeler's 

 consideration of available results led to the conclusion that com 

 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 e;reater 

 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 was 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 I^^orvegicum. Norges 

 Vaxtrage. Et Bidrag til N"ord-Europas l^atur-Og Kulturhis- 

 torie.l. Christinia, 1885. Rev. in Bot. centralb. :28 203.1 886.; 



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 on cold ex- 

 posure is undoubtedly the predominating one, but the minimum, 

 the range in variation, and the occurrence of minima below the 

 freezing point during the vegetative season, are also of import- 

 ance in distribution and await the acquisition of additional data 

 before their interpretation may be attempted successfully. Some 

 of these factors are extremely localized, and the poleward limit 

 of distribution in the northern hemisphere of many species is 

 known to run in extremely irregiilar lines. 



Some illustration of this is gained from the results of the 

 comparative study of the climate in the hemlock grove of the 



