WATER REQUIREMENT OF DIFFERENT KINDS OF PLANTS. 
73 
The results are of interest chiefly because of the early date at which 
they were obtained. It is evident that Lathyrus made very little 
growth but continued to transpire, thus increasing its water require- 
ment. 
LAWES'S EXPERIMENTS. 
Lawes (1850) was the first to make a careful comparison of the 
water requirement of crop plants. The results of his experiments 
have been discussed and are given in Table XXI (p. 31). The water 
requirement of the different plants measured is summarized in 
Table LXIV. 
Table LXIV 
Water requirement of crop plants i)i England, according to Laves (1850. 
p. 54). 
Oop. 
Culture. 
Number of 
determina- 
tions. 
Mean dry 
matter." 
Water re- 
quirement. 
Remarks. 
Wheat 
Barlev 
Clover 
Soil 
do 
do 
3 
3 
3 
Grams. 
25.3 
27.6 
11.4 
225; 
262 
216 ! 
^Comparable. 
Wheat 
Barley 
Beans 
Peas 
do 
do 
do 
do 
do 
2 
2 
2 
2 
2 
29.1 
31.3 
34. B 
28.5 
14.2 
235 
258 i 
214 
235 
2.51 
Do. 
No probable error can be applied to these results, since three series 
of determinations were made, one with manured soil, one with 
unmanured soil, and one with soil containing mineral manure. The 
wheat, barley, and clover were treated in the same way and the 
results are directly comparable. The results show but little differ- 
ence in the water requirement of the different crops. In the order of 
increasing water requirement the crops are beans, peas, wheat, 
clover, and barley. These results agree with those of the writers in 
placing the water requirement of barley above that of wheat. 
wollny's experiments. 
Wollny (1877) determined the water requirement of a number of 
plants. He grew the plants in small zinc cylinders of two sizes, 
20 centimeters in height and either 22 or 13 centimeters in diameter. 
Each cylinder was provided with a cover, in the center of which a 
tube 2.5 centimeters long and 3 or 4 centimeters in diameter was 
soldered. The seeds were planted directly below the tube. The 
cylinders were kept on the west side of a house provided with an 
overhanging roof to protect them from the ram. They were weighed 
every three days, and the water lost was replaced. A correction was 
made for the water lost through evaporation from the soil by weigh- 
ing pots provided with similar covers but containing no plants. 
285 
