550 
AMERICAN JOURNAL OF BOTANY 
[Vol. io, 
or oxide to the silt soil than to the sandy soil in order to produce the same 
changes in reaction. The difficulty of obtaining any marked alkaline re¬ 
action with the carbonate has already been mentioned. It was even neces¬ 
sary to add what would ordinarily be considered excessive amounts before 
neutrality could be produced. Sharp and Hoagland (19) have observed 
that 
Some soils whose solutions are neutral or alkaline remove considerable quantities of 
calcium hydroxide from the solution without materially increasing the OH-ion concentra¬ 
tion of the soil suspension. In certain cases this reaction might be erroneously attributed 
to soil acids. 
It seems evident, therefore, that the actual reaction produced in the soil 
should be the basis for forming conclusions concerning the effects of liming 
soils, rather than the uncertain reaction produced by some amount of lime 
added as calculated by means of the various lime-requirement methods. 
Judging from examinations of infected plants and the rapidity with 
which the disease develops, the critical period of infection in the seedlings 
appears to occur within the first few days following germination. The 
primary xylem was always found to be affected, and, as the result of this 
observation in experiment 1, it was decided to determine the reaction of the 
soil at planting time in the later experiments. 
A difference in size was the most conspicuous variation in plants grown 
at pH 5.6-5.8 to 7.0-7.4; the smallest plants were produced in the acid 
soils. A very uniform gradation occurred until the neutral point was 
approached. At this point the largest plants were produced. At hydrogen- 
ion concentrations greater than about pH 5.6, germination was slightly re¬ 
tarded and somewhat less uniform. Usually the plants produced in the 
more acid soils were slightly lighter green in color, but this condition was not 
consistent. These variations in growth appeared to be due more to differ¬ 
ences in nutrition than to the direct effect of acidity. It is well known that 
the general fertility of acid soils is affected favorably by the use of calcium 
carbonate.. In this connection also, Truog (21) believes that “it is usually 
because the actual lime needs of the plant are not fulfilled that soil acidity 
exerts a specific injurious influence on certain plants, and not because the 
acidity is directly toxic or destructive. ” 
Observations on the growth of plants in alkaline soils were very limited, 
since in only two cases was any degree of alkalinity secured. It will be re¬ 
called that the plants in flat no. 5, experiment 3, made a very poor growth 
in soil testing pH 8.2. The leaves were very dark green and the stems were 
very small and woody. In this case the detrimental effects may have been 
due in part to an excess of lime without sufficient magnesium. It is im¬ 
probable that the effects were caused by soil sterilization, since plants were 
normal in the other flats of the series. In experiment 4 the growth of the 
plants was considerably slower in the sandy soil testing pH 8.2 than at 
pH 7.2. It is interesting to note in this general connection that Hoagland’s 
