18 EXPERIMENT STATION RECORD. 



humidity is discussed. It is there sliown tliat lioweriug is retarded by 

 dry soil or humid air and hastened by dry air and liumid soil. 



As regards increase in weight, the author's experiments show also that 

 humidity, and especially excessive irrigation, is very harmful to j^lauts 

 in'^ended for seed production. On Avet soils the seeds are somewhat 

 moic numerous, but snuiller and subject to rapid degeneration. Dry- 

 ness of the soil in compelling the individual to grow slowly and by" 

 decreasing considerably the number of its descendants strengthens the 

 species and protects it against external influences causing variation. 



Tiie same conclusions were reached relative to tubers. Excessive 

 moisture weakens the race while apparently favoring the individual by 

 increasing its growtli. The tubers are heavier, but are less i^erfect thau 

 those which are i)roduced under drier conditions. 



PRACTICAL APPLICATIONS. 



According to King,i after a rain, soil to a depth of a meter and a half, 

 contains about 0,000 tons of water per hectare, the greater i)art of which 

 is carried off by evaporation. Cultivation is very efiicacious in preserv- 

 ing tliis water. Professor King determined ou April 118 the quantity of 

 water contained in two contiguous soils, afterwards plowing one of 

 theui. Seven days later the water content was examined to a depth 

 of 1.2 meters. The ])lowed soil had lost from the upi^ei' 30 cm. 11 5 

 tons per hectare, and there was a gain of the same quantity of water 

 for the succeeding 90 cm. The unplowed soil, on the contrary, to a 

 depth of 1.2 meters, had lost 495 tons of water. Spring plowing, there- 

 fore, conserves the humidity necessary for plants, but although this 

 plowing is very eflicieut, harrowing and scraping poorly done is not. 

 Harrowing which simply scratches or furrows the surface without cov- 

 ering it completely with loose soil increases evaporation rather than 

 reduces it. On the contrary, a layer of dry soil 2 cm. dee}) greatly 

 reduces evaporation. 



When a given soil produces vigorous plants whose transpiration is 

 very active and young plants whose organs are less developed, the roots 

 of the first will take up lor themselves the humidity of the soil with 

 grenter force than those of the second. If the soil does not contain 

 sufficient water for both, the weaker will suffer. This is the case with 

 clover seeded with wheat in the autumn, which suffers in a dry spring, 

 while clover seeded alone makes good growth. Farmers continue to 

 sow their forage seed with cereals under the mistaken idea that the 

 cereals are beneficial as a shade. If they would seed their forage jdants 

 alone, they would not only secure a greater yield but in dry countries 

 they would stand a better chance of producing a crop. 



This also explains certain facts relative to the irregular production 

 of seed of the same kind pf i)lants. The stronger plants take from the 

 others the moisture and the fertilizers held in solution, and are thus 



'Wiscousiu Sta,. Rpts. 1891, p. 100; 1893, p. 184 (K. S. R. 4, p. 122; 7, p. r,m). 



