Roots and its Influence on the Ecesis of Plants in Swamps . 2 7 
a supersaturated soil than in water alone, and a much greater difference 
exists between a supersaturated soil and an ordinary soil. This accounts 
for the observations of Wacker ( 25 , p. 109) that seedlings of Vicia Faba and 
Lupinus albus grown in supersaturated soil showed as compared with’ the 
amount of growth in moist soil a greater retardation even than when grown 
in water. He observed, however, that with frequent changing of water the 
retardation was somewhat less. 
Oxygen diffuses slowly through water, so that the supply is not quickly 
replenished by diffusion alone. The investigations of Kraus ( 13 ) show that 
boiled water in vessels sealed to exclude the air completely prevents the 
germination of seeds. Boiled water exposed to air after eight days gave 
a greatly reduced percentage of germination as compared with seeds in 
unboiled water. The amount of root growth was also much less in the 
former than in the latter. He also shows that submergence at greater 
depths decreases the percentage of germination of seeds, which he explains 
by the slowness of diffusion of oxygen. In open water agitation by wind 
and convection currents tend to replenish the oxygen supply. These 
factors are probably more important than diffusion. In supersaturated soil 
convection currents and surface agitation are not factors, or are of very little 
importance. 
The very small amount of oxygen in the substratum of peat or 
Sphagnum swamps is also to be explained by the difficulty of replenishing 
the supply from the air. In peat or Sphagnum substrata the presence of 
living Sphagnum and of the accumulated remains of dead plants prevents 
surface agitation of the water and convection currents by which the oxygen 
content could be maintained. There is also another factor which operates 
here, and which does not affect the aeration of ordinary soils, or only to a 
slight extent. This factor is the presence of partly decomposed remains of 
Sphagnum and other plants, which absorb the oxygen and prevent its pene- 
tration into the deeper-lying parts of the substratum. Dachnowski (5, 
p. 37a) calls attention to the reducing power of peat, and shows that it is 
greatest in the central zone and decreases towards the outside. 
In comparing the growth of various plants in soil, peat, and Sphagnum , 
with the roots submerged, it was noticed that the roots of plants in peat 
were usually more retarded in growth than those in soil, and that those in 
Sphagnum showed the greatest retardation. A similar relative reduction in 
growth of parts above ground was observed. An explanation for this did 
not at first suggest itself. Later it was found, in the experiment described 
on p. 21, that only a slight difference in the size and vigour of shoots was 
noticeable between plants watered with swamp water and those watered 
with culture solution. The roots, moreover, were equally well developed in 
all plants. The difference could not have been due to a lack of aeration 
since oxygen was available to the roots at all times. The difference was 
