231 
sunshine alone fail to give a sufficient explanation. Finally, a natural 
and sufficient explanation is found in the study of the relation of the 
rainfall in summer to the given climatic conditions, as has already 
been done in the study of the heat; it is not the rainfall of the spring 
months that stimulates the plant, but it is the drought of the suc- 
ceeding summer, or, as it were, the knowledge of that approaching 
drought which stimulates the plant to hasten and complete its devel- 
opment in the springtime or earliest summer. The plants of the 
north are accelerated because of the rapidly approaching autumn; 
the plants of the highlands because of the shortness of the approach- 
ing summer; the plants of the steppes and of regions with rainless 
summers hasten in order to have their work finished when the time 
arrives at which their activity should come to an end. The plants at 
localities in our zone B complete their labors in the springtime be- 
cause of the drought of the coming summer; under almost the 
same external conditions the plants at Parma hasten their develop- 
ment while those at Venice live leisurely along; the plants at Vienna, 
Breslau, and Kief accelerate their growth, while the same plants at 
Heidelberg, G6rlitz, and Orel live leisurely. 
The problem, so often discussed, of the reforestation of the steppes 
is thus referred back to another more definite problem, viz., the 
acclimatization in the steppes of those plants whose normal cycle of 
vegetation in their native locality is such that when transplanted 
to the steppes these processes, especially the blossoming and leafing, 
can go on with sufficient rapidity to be completed before the begin- 
ning of the hot, dry summer. Quite similarly the problem of culti- 
vation of fruit in those regions can be thus exactly defined. Thus 
Helmersen states that experiments with fruit trees brought from 
Hamburg to Orenburg entirely failed. But here we have to do with 
a double violation of the theory, since the plants brought from Ham- 
burg came to a locality having a much smaller annual sum of heat 
and were not yet adjusted to the dryness of the Orenburg summers, 
wherefore they continued living at Orenburg according to the easy 
habit acquired at Hamburg. Lainsser suggests that success would be 
much more likely if plants were taken to Orenburg from Bokhara or 
Khiva, where the extraordinary rapidity of development, on account 
of the great dryness of the summer following after a rainy spring is 
well known. 
Further questions as to the temporary influence of rainfall during 
any part of a cycle of vegetation must be investigated by studying 
the hfe of plants at localities having very different climates. 
After studies on the development of vegetation in various climates 
throughout the world, in all of which the rainy season is the blossom- 
