132 
FLORIDA STATF GEOLOGICAL SURVEY. 
To the evaporation from the surface of the soil must be added 
that from the leaves of plants. This in turn varies greatly with 
the different plants and with different climatic conditions. King, 
in 1892, in one experiment, found that a crop of peas evaporated 
477 pounds of water for each pound of dry matter formed, while 
•corn under the same conditions evaporated in one instance 238 
pounds of water per pound of dry matter.* Assuming that a 
citrus tree evaporates approximately as much as the European 
oak (Quercus cerris), the water evaporated from the leaves of a 
fifteen-year-old orange tree is estimated, by Hilgard, at 20,000 
pounds a year, or about 1,000 tons of water per acre of 100 trees.*)* 
This is equivalent to about nine inches annual rainfall over the 
same.area. Water is the chief vehicle for conveying plant food 
absorbed from the soil by the roots. This enormous evaporation 
from the leaves is in part for the purpose of disposing of the 
water thus taken up by the plant. It serves chiefly, however, the 
purpose of preventing, through the conversion of water into vapor, 
an injurious rise of temperature during the hot sunshine and dry 
weather. 
It is impossible to estimate within even approximate limits 
the loss of water by evaporation from the surface of the ground, 
and from the leaves of plants in the area under consideration. 
The atmosphere in Florida is relatively humid. On the other 
hand, the temperature throughout most of the year is high. Much 
of the country is uncultivated, and practically all of the soil is of 
medium coarse texture. 
It is probable that almost one-half of the rainfall entering the 
earth is re-evaporated from the surface of the ground and from 
the leaves of plants, and that not more than one-half of the total 
rainfall in Florida passes through the soil and surface material 
to join the underground water supply. 
*20th Ann. Report Wis. Agriculture Experiment Station, p. 320 ,1904. 
fBased on weighings made by R. H. Loughridge of the leaves of a 
citrus tree at Riverside, Calif. Soils, by E. W. Hilgard, p. 263, 1906. 
