The following paper was read by D. T. MacDougal : 



Factors Affecting the Seasonal Activities of Plants. 



By Dr. D. T. MacDougal, 

 The Desert Laboratory , Tucson, Arizona. 



DISTRIBUTION AND ACCLIMATIZATION. 



Every species inhabits the areas which it has been able to 

 reach and occupy from the starting point of its place of origin. 

 Neither its birthplace nor any of the places within its range may 

 offer the most suitable conditions for the best growth and highest 

 development. Beyond seas, over mountain ranges, across the 

 equator or past other equally effective barriers may lie plains, 

 valleys, plateaus or even continents, where if once introduced, 

 it might overbear all competition from the plants already there, 

 extending its distribution a thousand-fold and the number of its 

 individuals a million-fold. Let the barriers be but once passed 

 and it enters into a new kingdom, as the various invasions of 

 weeds amply testify. 



The soil, the various factors of climate^ the course of the 

 seasons, and the actual composition of the plant-covering already 

 present in the region, may be such that the intruder becomes an 

 integral part of the flora, and it may indeed perish in its origi- 

 nal habitat and in the places successively occupied by it, leaving 

 us no clew as to its place of origin. 



The value of a cultivated plant is fairly co-ordinate with 

 the extent of its possible distribution and culture. Not only 

 does its greater cultivation bring a greater total product, but the 

 greater the crop the better developed may become the facilities 

 by which it and all of its constituents are used to the fullest, and 

 to the greatest economy by the human race. 



Our conscious efforts to widen the range of distribution and 

 extent of cultivation of species of interest and economic value 

 facilitates and aids one of the most basal processes in the life of 

 the plant, and it has before it the possibilities of limitless sue- 



