which the book of nature is written. Since the prehistorical times man has felt that vege 

 tation is the most sensitive indicator of climate, but only now are we beginning to suc- 

 ceed in the decoding. 



In less poetical form, we can say that these three fundamental laws and the four 

 biological methods derived from them supply us with quantitative solutions of geophy- 

 sical problems by plantecological means. These methods are well on their way to play- 

 ing an important role in the work of making the desert areas of the earth productive. For 

 in these areas we are very near to the limit of plant survival in general, and the plants 

 react therefore in a most sensitive way to the minutest changes in their environment. 

 Because of this it is much easier here than in the humid regions to exploit this sensi- 

 tivity for practical purposes. Nevertheless, in this field as in so many others, there 

 must be, of necessity, close international co-operation in order to reduce errors to a 

 minimum, and to apply practical results on a global scale. 



One thing is certain, that symposia and discussions such as we are having here at 

 the Institute of Biology in co-operation with UNESCO, are the best way to reach this 

 objective. 



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