1921] EMERSON—BOG PLANTS 367 
MarkKLeE (6) working in New Mexico, and WEAVER (9, 10) in 
the prairies, have noted that two dominant species in an associa- 
tion are not likely to have their roots so placed as to have any 
marked subterranean competition. This is obviously not the case 
in the main parts of this bog flora, where two codominants, Vac- 
cinium macrocarpon and Aspidium Thelypteris, have practically the 
same level, and together dominate the greater area of the bog. 
Neither of these two dominant species seems to be overcoming the 
other. Mingled with these are a number of less important species 
also at the same level. On the other hand, the deep-rooted forms 
in which there is no competition are in no case crowding out the 
shallow rooted species. 
Aerenchyma is very common both above and below the water 
table. Roots and rhizomes which grow below water are all very 
rich in air tissue, with the exceptions of Betula pumila and Salix 
spp. In these species no aerenchyma was found in any of their 
parts, nor, with the exception of Decodon verticillatus, was it found 
in any woody perennial examined. In most cases herbaceous 
species have a great deal of aerenchyma. 
Tests for H ion concentration in the soils were made by means 
of the colorometric indicators made by the La Motte Chemical 
Products Company. The records were made in terms of specific 
reaction (11). The tests were made in the white porcelain “spot 
plates,” such as are commonly used in the chemical laboratory. 
By means of pipettes the water to be tested was drawn off from 
the absorbing parts of the roots. In all cases fruiting or flowering 
plants were used. Both pipettes and spot plate were thoroughly 
rinsed in the water to be tested before beginning each test. 
series of samples was taken across the bog from the lakeward margin 
toward the landward side. The water of the lake was uniformly 
30 alkaline. The reaction on the floating mat gradually changed 
from alkaline to neutral, and finally reached 10 acid, 2 or 3 m. from 
the lakeward margin. This reaction was uniform across the entire 
mat until the decaying peat was reached on the landward side. 
Here the acidity decreased until it reached neutrality at a point 
where the mat was so decomposed that it would no longer bear the 
weight. It was not possible in any case to discover a difference in 
