106 BOTANICAL GAZETTE [FEBRUARY 
indicative of superior conditions for growth, and undoubtedly con- 
tribute largely to the increased transpiration. 
The general effect of treatment by an absorbing agent in case of 
soil extracts also is to increase transpiration and root growth of the 
plants, although there are occasional cases where the increased trans- 
TABLE VIII. 
EFFECT ON TRANSPIRATION OF TREATING VARIOUS SOIL EXTRACTS WITH 
ABSORBING AGENTS BEFORE USING THEM AS CULTURE MEDIA* 
Units water rn 
No. Soil extract Transpiration | Green weight or stg j 
weight 
1 | Elkton silt loam 178 107 167 
2 | Lyons silt loam 95 121 81 
3 | Alloway clay 405 147 316 
4 | Kingston soil 81 97 
5 | Takoma lawn soil 190 104 182 
6 | Arlingt il 142 IIo 128 
7 | Dunkirk sandy loam 87 110 
8 | Memphis silt loam 154 118 129 
g | Arlington clay lo: 108 IIo 97 
1o | Takoma lawn soil 137 109 125 
tr | Kingston soil 116 109 106 
12 | Memphis:silt loa 117 99 119 
13. | Dunkirk sandy loam 114 114 1 
14 | Arlington clay loa 158 102 155 
t5 | DeKalb silt loam 133 103 126 
16 | Cecil sandy lo: 112 97 108 
17 agerstown loam 229 102 225 
18 | Dutchess silt loam 216 89 122 
tg | Cecil sandy loam 193 114 17 
20 | Lyons silt loam 226 131 181 
2I enn clay 402 Tir 364 
22 | Miami black clay loam 142 98 144 
23 | Miami silt loam 172 123 139 
24 | Lyons silt loam 626 135 _ 461 
25 | Park soil 136 97 153 . 
Perc 
Average 185.3 108.8 164.2 
i eee 
* The absorbing agent used for treating the first 19 soil extracts was carbon black; for the 
remainder ferric hydroxid was used.. 
piration is small or negative. Table VIII presents the results of a 
number of experiments upon this question in which a variety of 
soil extracts were used. The results of the experiments, made at 
different times, are presented in terms of the growth of plants grow? 
in control cultures. These control results (not presented in te 
table) were always taken as roo, and the response to treatment with 
the absorbing agent expressed by proportional figures. 
