1 8 Bergman. — Relation of Aeration to Growth and Activity of 
those in peat intermediate. In submerged plants less difference was notice- 
able, although the same order seemed to hold. Loss of leaves did not 
occur in any of the plants. Removal of the cotyledons caused a general 
reduction in the amount of growth. This was least noticeable in plants 
grown in moist garden loam, and quite evident in plants grown in peat or 
Sphagnum . The reduction in growth was most noticeable in plants grown 
in peat or Sphagnum with the roots submerged. 
Plants grown in moist soil showed the greatest development of roots. 
The form of the root system of plants grown in either peat or Sphagnum 
was similar, and in extent of growth nearly equal to those in soil. The 
roots of all plants under conditions of submergence were similar. The 
lower roots were dead, and new roots had developed from the stem at the 
surface of the ground. The depth of -penetration was never more than an 
inch below the water surface. The longer and more branched roots usually 
came even nearer the surface. No root-hairs were present on submerged 
roots, although abundantly present on others. 
Effect of Root Submergence on Transpiration. 
The following experiment was performed to ascertain the effect of 
root submergence on transpiration: Two plants of Pelargonium ; potted in 
soil, were placed in aluminium pots, the tops of which were covered with 
Fig. i. Graphs showing comparative rates of transpiration of two plants of Pelargonium, the 
broken line for the one in moist soil and the solid line for the one in soil submerged. The break on 
the sixth day marks the time at which the roots were submerged. On the eleventh day the leaves 
began to turn yellow, and by the fourteenth day were beginning to drop off. A decrease in the rate 
of transpiration is evident on both of these days. 
sheet rubber to prevent evaporation from the surface of the soil. The 
plants were weighed each day for a week. The roots were then submerged 
and the daily weighing continued. The results are shown in the accompany- 
ing graph (Fig. i). On the day following root submergence it was found 
that the rate of transpiration had greatly increased. The rate, however, 
fell off rapidly, and after two days had fallen to a point lower than 
when growing in moist soil. Recording instruments showed that the 
humidity and temperature conditions in the greenhouse had not changed. 
