HYGROSCOPIC WATER 63 



soil as will maintain the plant cells in a turgid condition. 

 It is of course possible that if changes of temperature are 

 allowed, the amount of water condensed by the soil may 

 suffice for the maintenance of a plant ; but it is not true that 

 a soil containing only hygroscopic water is capable of main- 

 taining plant life, and this has been abundantly proved by 

 the investigations of Heinrich, A. Mayer, Liebenberg, and 

 Hellriegel (Jahresb. Agrik. CJiem. 1875-6, 368). 



Heinrich grew plants in very small boxes till fully 

 developed, and then placed them under conditions of very 

 little evaporation till they began to wilt ; the soil in the box 

 was then mixed, and the proportion of water it contained 

 determined. A variety of soils were employed. A weighed 

 quantity of each soil was also placed in a dry state in 

 a saturated atmosphere till it ceased to gain weight, and the 

 amount of hygroscopic water which the soil could absorb was 

 thus determined 1 . It was found in every experiment, that 

 when the plants wilted the percentage of water in the soil 

 was still somewhat higher than that proper to hygroscopic 

 water only. The figures given in Table VII show the average 

 results obtained with oats and maize. 



Experiments made with grasses, with various leguminosae, 

 and with potatoes, gave similar results. The potatoes grown 

 in peat required 41-4 per cent, of water in the moist peat, or 

 70-8 per 100 of dry peat, to avoid wilting 2 . The leguminous 



1 The hygroscopic water found would have been higher had the soils 

 been dried at 200 C., but this fact will not alter the conclusion drawn from 

 the experiment, as the amount of water remaining in the soil after the 

 growth.of the plant would in that case have also to be determined at 200 C. 



2 In experiments on the growth of crops on peaty land it has been noticed 

 that the peat must contain more than 60 per cent, its weight of water to yield 

 productive crops (Biedermann's Central-Blatt fur Agrikulturchemie, 1885, 297). 



