THE FKEK WATEK OF THE SOIL. 209 



water Is continually carriccl from the atmosphere into 

 vegetation. 



In a similar experiment, a tobacco plant was employed 

 ■which stood in a soil of humus. This material was also 

 capable of supplying the plant with water by virtue of 

 its hygroscopic power, but less satisfactorily than tlie clay 

 As already mentioned, these plants, while remaining fresh,, 

 exhibited no signs of growth. This may be due to the 

 consumption of oxygen by the roots and soil, or possibly 

 the roots of plants may I'equire an occasional drenching 

 with liquid water. Further investigations in this direc- 

 tion are reqiiired and promise most interesting results. 



What Proportion of the Capillary and Hygroscopic 

 Water of the Soil may Plants Absorb, is a question that 

 Dr. Sachs has made the only attempts to answer. When 

 a ])lant, whose leaves are in a very moist atmosphere, wilts 

 or begins to wilt in the night time, when therefore trans- 

 piration is reduced to a minimum, it is because the soil no 

 longer yields it water. The quantity of water still con- 

 tained in a soil at that juncture is that which the plant 

 cannot remove from it, — is that which is unavailable to 

 vegetation, or at least to the kind of vegetation experi- 

 mented with. Sachs made trials on this principle with 

 tobacco plants in three different soils. 



The plant began to wilt in a mixture of hlack huniKS 

 (from beech-wood) and sand^ when the soil contained 

 12.3" |„ of water.* This soil, however, was capable of 

 holding 46° |„ of capillary water. It results therefore that 

 of its highest content of absorbed water 33.7" |„ (=46-12.3) 

 was available to the tol>acco jjlant. 



Another plant began to wilt on a rainy night, while the 

 loam it stood in contained 8°| „ of water. This soil was 

 able to absorb 52.1°! ^ of water, so that it might after 



Ascertained liy diyiiija'at 31 



