334 BOTANICAL GAZETTE {aw 
was produced by B. 13; the least amount was recorded for Bg. w. 1%, 
the culture solution, it will be remembered, which consisted of a 
mixture of the bacteria found in 1°° of fresh bog water. None of 
these products were found in the control (sterilized bog water and 
peat). It is also to be noted that in the various pure bacterial cul- 
tures neither the organic acids nor the ammonia underwent a further 
change; in the mixed cultures, however, the decomposition con- 
tinued, the amido-acids being formed to ammonia and to compounds 
of the fatty acid series. The extent to which the latter substances 
may be still further disintegrated to carbon dioxid, hydrogen, and 
methane is now being determined. Thus far the isolation of bacteria 
involved in the decomposition of carbohydrates has not been suc- 
cessful. Certain microorganisms have been found to possess the 
ability to dissolve cellulose (filter paper) in the presence of air. To 
what extent these forms and the anaerobs play a réle in the relation 
of deleterious products in the soils and the cultivation of crops is 
still uncertain. In a previous paper (Bot. GAZETTE 47400. 1909) 
the writer has reported that the poisonous matter injurious to plant 
growth is present in the agricultural soils used as filters for bog 
water. The retardation seen in the contaminated soils lacked the 
corresponding control average in dry weight of plants to an amount 
of 18 percent, 3 per cent, and 36 per cent, for sand, clay, and humus 
soil respectively. It was further shown that the absorption and 
retention capacity of soils for toxins became generally higher the 
greater the content in humus. 
In concluding this part of the discussion it is well to note the 
extent to which the results show clearly that, in the laboratory cul- 
tures at least, the retardation in growth of wheat plants is not cau 
by physical or chemical conditions, but through the direct activity of 
the bacterial flora upon the peat substratum. 
It has long been suspected that a reciprocal relation exists between 
groups of soil bacteria and the plants growing upon the soil. Various 
writers have been able to point out that marked differences in the 
productive power of different soils followed the growth of wild plants, 
and that these differences persist for some time. It is generally com 
cluded, therefore, that the injury caused to cultivated plants by weeds 
or previous crops is due to influences on the bacterial life in the soil, 
