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sunshiiio alone fail to give n sufficient explanation. Finally, a natural 

 and sufficient explanation is found in the study of the relation of the 

 rainfall in summer to the gi^^en 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 Avhen 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, Gorlitz, 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. Linsser 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 drjaiess 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 life 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- 



