233 
perature for the same phases of plant life from year to year, and 
the reason of their variations. On this last 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 following 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 would occur if the plants 
remain in Stuttgart and we 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 years. 
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 chmate. For 
instance, in general it is desirable to sow and plant so as to avoid 
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 will ripen in the earliest summer, 
before the droughts destroy them, as in the region from Nebraska to 
Texas, then we 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 always be preserved for 
sowing, 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 1s, 
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 
