DROUGHT. 



515 



the height-growth (1893) ; at its close, it reduces radial growth 

 (1887). Dry years, as well as frost years, may be detected on 

 the transverse sections of a bole by narrow annual zones. 



Professor Henry,* of Nancy, measured 250 trees in order to 

 ascertain the loss of diameter increment, in the very dry 

 summer of 1893, with the following result : 



Occasionally single stems, or groups of poles, may be 

 killed by insolation ; this is frequently the case with beech 

 standards, which after growing in a dense wood are exposed, 

 as mother-trees, in seeding-fellings. The yield of dead wood 

 in dry years is very considerable. 



In seasons of drought plants cannot obtain sufficient nitrogen 

 compounds from the soil; E. Mer also proved that starch- 

 production in the leaves is weakened. Plants by premature 

 leaf-fall also suffer a considerable loss of combined nitrogen and 

 phosphoric acid, that prejudices the formation of fruit and seed. 



Professor Krausf analysed the leaves of lilac, Conms mas, 

 L., and horse-chestnut with the following results : 



" Rev. des E. et F.," 1895, p. 75. 



I " Die Sommerdurre der Baume," " Central Blatt fur das Gesammte Forst- 

 wesen," 1875, p. 206. 



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