30 Bergman . — Relation of Aeration to Groivth and Activity of 
to grow when submerged to a depth of one inch. Fruits of Typhd , 
Sagittaria , and Alisma germinate and develop readily under water. It 
was observed, however, that fruits of Alisma and Sagittaria in jars of 
water with clean sand at the bottom failed to develop beyond the early 
stages of germination. The oxygen and carbon dioxide content of the 
water was not determined, and consequently it is not known to what extent 
the concentration of these gases may have been responsible for the failure 
of the seedlings to develop. 
Car ex pseudocyperus, Dulichium arundinaceum , Ribes spp., Salix spp., 
and many other plants germinate readily on hummocks of Sphagnum or on 
mounds of peat, but fail to germinate if submerged. Seedlings of Andro- 
meda glaucophylla , Kalmia glauca , and Ledum groenlandicum have been 
found on Sphagnum or peat above the water-level. It seems probable, 
therefore, that seedlings of these plants are not able to develop under 
prolonged root submergence. Gluck (9) found that the seeds of many 
plants possessed the ability to germinate and grow under water. Other 
seeds failed to germinate if covered to a depth of half an inch or less. 
Kraus (13) has shown that the germination of seeds of land plants may be 
brought about by aerating the water. Differences are to be observed in the 
behaviour of various seeds in this respect. Some require less oxygen than 
others. 
The behaviour of roots of seedlings shows the same relation to aeration 
that is shown by the roots of older plants. Only those plants with well- 
developed aerenchyma are able to establish themselves in habitats with an 
excess of water. If the water-level is below the surface slightly, many 
plants are able to invade and become established. The roots of such 
plants remain near the surface. Periods of hot, dry weather during the 
summer, which cause the upper layers of the substratum to become dry, may 
then result in the death of seedlings with shallow root systems. Thus it is 
evident that the need for adequate aeration for the germination of seeds 
and the development of seedlings is an important factor in ecesis. It 
determines in a large measure the character of the invaders in swamps. 
Conclusions. 
(1) Roots of land plants do not live under prolonged submergence. 
The submerged foots die and new ones are developed from the stem at the 
surface of the water. This occurs whether the plants are grown in loam, 
peat, or Sphagnum. 
(2) Land plants grown in peat or Sphagnum show an evident reduction 
in growth of the entire plant when the roots are submerged. This is little 
or not at all apparent in plants grown in soil with submerged roots. 
(3) Reduction in growth of plants in Sphagnum with the roots sub- 
