84 BOTANICAL GAZETTE [FEBRUARY 
The data to be presented in this paper were drawn from upward 
of 6000 tests employing soils, soil extracts, and salt solutions. The 
data showing the effects of treatments upon soils were obtained 
from experiments which employed 189 soils from various parts of 
the United States. These data were obtained in the course of 
fertility tests made by the Bureau of Soils of the U.S. Department 
of Agriculture, and were kindly furnished by Mr. F. D. GARDNER, 
who was in charge of the work; the other data are drawn from 
a b c d é 
Fic. 1.—Method of making paraffined wire pots: a, wire frame; 6, same ie 
m of paraffin; c, same filled with soil; d, completed pot, having wall gangs 
repeated dipping in melted paraffin; e, pot containing plants four days old anc s 
ing the cover of paraffined paper sealed to rim of the pot. 
experiments made by the author while a member of the staff of 
that bureau’s laboratory.* 
All tests conducted with soils were made in the standard paraffin 
wire pot employed extensively for experimental work in plant mr 
ology and agronomy. As an instrument of research it nee 
itself especially because of its easy construction and its ability to yiel 
accurate experimental results.? 
The method of making these pots is illustrated by fig. 7. in 
framework of wire netting is ro°™ in diameter and of the same eee 
(a). After coating the rim of the framework by dipping seveT@'. 
' For making most of the computations upon which this paper is based, I am 
indebted to my wife, Hannan D. REED. 
his es 
1908, p. 173. 
2d ed., 
es 
y mention in GANonc’s Plant physiology, 
