233 



perature for the same phases of phmt life from year to year, and 

 the reason of their variations. On this hist point he concludes by 

 stating that it is well known these sums do vary from year to year 

 for each phenological epoch. For the present he states only that 

 these temperature sums are not only apparently, but in reality, not 

 constant, and from his preliminary work for this second series of 

 studies the most important causes that determine the sum total had 

 already become known to him. Without anticipating too much the 

 course of further investigations, he states that studies already finished 

 demonstrate that there should be differences annually in the tempera- 

 ture sums, as is evident from the folloAving consideration : If seeds 

 brought from Stuttgart to Christiania accelerate in successive gener- 

 ations in successive years because of the smaller sum total of heat 

 in their new home, then exactly the same w^ould occur if the plants 

 remain in Stuttgart and w'e at that place offer them the sum total of 

 heat peculiar to Christiania. That is to say, seeds that have ripened 

 at any one place in colder years produce plants that develop more 

 rapidly than do seeds from the same place but which were ripened in 

 warmer j^ears. 



APPLICATION OF LINSSEr's RESULTS. 



This application to each plant and each locality of the principle of 

 economy which Linsser had established from the geographical dis- 

 tribution of plants offers to us by far the most important principle 

 yet discovered and well established to guide us in the development of 

 grains and plants appropriate to the vicissitudes of our climate. For 

 instance, in general it is desirable to sow and plant so as to avoi(^ 



the early autumn frosts and the late spring frosts — that is to say, to \ ^ 



secure varieties of plants whose course of vegetation will be complete 

 in the very short time that is free from danger of frost. Therefore, 

 if we wish to develop plants that wall ripen in the earliest summer, 

 before the droughts destroy them, as in the region from Nebraska to 

 Texas, then Ave have to remember that the seed perfected in Kansas in 

 a dry year is already, by its own experiences, prepared to become the 

 best seed for sowing in anticipation for the next dry year. The 

 seeds raised in dry years should therefore alwaj'^s be preserved for 

 sow-ing, as likely to be far more appropriate than any seed that may 

 be brought from a distance, unless brought from a region where 

 equally dry, short seasons prevail, as in southern Russia and Bokhara. 

 The rule of sowing one year the seed raised the preceding year is, 

 in general, not the best rule. By always utilizing as seed that which 

 is raised in the driest years one may hope speedily to develop plants 

 whose vegetating period will be so short that the crop will rarely be 

 injured by the dry, hot winds of July. A similar rule holds good 

 for any modification we desire to make in the seed. If we wish to 



