110 
AVAILABLE MOISTURE. 
In his investigations as to the relation of atmospheric precipita- 
tion, especially rainfall, to the plants and the soil, Wollny shows that 
the percentage of water in the layer of soil containing growing plants 
increases from above downward as soon as the downward movement 
of the rain water in the soil ceases, but that the percentage increases 
from below upward while the rain is falling and so long as the water 
continues to be penetrating downward. The frequency of rainfall 
is of even greater importance than the quantity. Shght rainfalls 
that only wet the soil to the depth of a few millimeters do but little 
good to the vegetation, because the greater part of the water is 
quickly evaporated back again into the atmosphere. If it should 
rain daily 2 millimeters during the three summer months, then, even 
with this abundant precipitation the plants might die for want of 
water, whereas if this total of 180 millimeters were uniformly 
divided into ten or twelve rains during the three summer months it 
would be considered a remarkably favorable growing season, since 
under these conditions the earth would be wet down to a considerable 
depth and the water thus stored up is protected from evaporation. 
Therefore, for equal quantities of rain its value for agriculture 
increases as the number of rainy days diminishes, and diminishes as 
the number of rainy days increases, at least up to a limit that varies 
with the character of the soil. 
Tn order to attain precise ideas on this subject, Haberlandt set out 
a series of glass tubes full of dry earth; each received at the begin- 
ning a certain quantity of water, and by weighing these from day to 
day he determined the loss due to evaporation. These losses are 
given in the following table, in percentages of the original quantity 
of water, which latter may be considered as a rainfall whose depth is 
given at the top of the column: 
| l 
Date. ake 2 3 VR Pee) 135 6 
a aT, iat Toe | a | | io 
Initial rainfall September 20 in millimeters. ---.-- | 2.22 6.67 | 13.33 | 26.67 | 40.00 53. 33 
Loss by evaporation in percentages. iF i | 
September 2iiites.c Tu, w le Pee) iat | 94.75 | 39.51] 26.34] 14.78) 9.81] 8.96 
September 222-2 4222-42 eee eee eae tee 5. 68 | 17.02 | 10.22 | 10.09 7.75 7.48 
Beptember eos: sate ete eae se eB ee eS eae | 18.85 | 14.87 | 13.39) 10.83] 9.05 
Septeniber 24 ae LD eee Ae AuBRvent |[Pemerese | 12.16] 14.56] 11.82] 8.99] * 8.09 
Sentember ons.) kos nl OM UES LUsteCee eae erase ae oie | {r7.29.1526. 20) A WEB0})> BIeT 7.05 
September 26-12 5.4 2 ssa ee ce ee eee Peed ee Se 3.04 |. (6:82))| 81% |) = 6592 6.7 
Sentem beret. s ai sees ae oe ee fee nee | 1.82] 5.89) 3.48) 8.51 3.48 
Repbem Denes ee One, te coe cnee ees seas ieee lr es eee ae Dien eaead Bei | 5.58] 3.65] 2.58 3.04 
Séptemberi29) 455. Be sce k Sane Sa Tee Me et Se ee | oe tel) Pare 2.96 1.86 2.61 
September 0 psa. wc sae ie ele ey ee er ee ene (rae 2.48) 1.74] 1.76) 2.00 
October ieee ste Fates ee ee ee ee feces ee 2.79) 5.55) 6.31) tz 
October lO ss ON le Me eee fesiees eso } 2.09| 2.89] 295 
Totaltin':20\days=osos225=2 sss Sse ae oe eee 100. 43 | 99.69 | 100.09 | 85.02 | 67.98 68. 63 
