180 HOW CROPS FEED. 
circulation of water in it, no continuous upward movement 
can take place without evaporation. The ease and rapid- 
ity of evaporation, while mainly depending on the condi- 
tion of the atmosphere and on the sun’s heat, are to a cer- 
tain degree influenced by the soil itself. We have already 
seen that the soil possesses a power of absorbing watery 
vapor from the atmosphere, a power which is related both 
to the kind of material that forms the soil and to its state 
of division. This absorptive power opposes evaporation. 
Again, different soils manifest widely different capacities 
for imbibing liquid water—capacities mainly connected 
with their porosity. Obviously, too, the quantity of liquid 
in a given volume of soil affects not only the rapidity, 
but also the duration of evaporation. 
The following tables by Schiibler illustrate the peculi- 
arities of different soils in these respects. The first col- 
umn gives the percentages of liguid water absorbed by 
the completely dry soil. In these experiments the soils 
were thoroughly wet with water, the excess allowed to 
drip off, and the increase of weight determined. In the 
second column are given the percentages of water that 
evaporated during the space of ‘four hours from the satu- 
rated soil spread over a given surface: 
Qari a SANG sa acciecacicietiysis' a siegeate Visjesietseesitnieds's 25 88.4 
Cry PSR saws sgikss Ka eAedeesa kanes to oka reahexawes 27 71.7 
AMG sBAN Go oo sic vtec tr sin heals etna ears tireetemays o unless 29 .9 
Dlaty Marlex scares saci was seee Gases naw teawe ceviee 34 68.0 
Clay soil, (sixty per cent clay,)............000008 40 52.0 
LO aM sera care weS8E2 dada enekacibcsiee, wick “ae teee 51 45.7 
PIOWSH ANG cli. cies ceeige eae Sesiva sages Riaied 8 52 32.0 
Heavy clay, (eighty per cent clay,).............. 61 34.9 
Pure Cray: Cla yes ncvicicnis vs on wughosowsee ive eed deae 6 70 31.9 
Fine carbonate of lime............ cece ec eee ee ee 85 28.0 
Garden: MOU: vison iecere wane douate's aaa vaeesGe 89 24.3 
FHS 3 cis aie casic ereieg esos shes Os Sawateniienasnetne si 181 25.5 
Fine carbonate of maynesia.............0000 eee 256 10.8 
It is obvious that these two columns express nearly the 
same thing in different ways. The amount of water re- 
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