78 DEAD ROOTS. [CH. Ill 



pressure by the drops of water exuding from the leaves. 

 Root pressure may as Moll has shown ^ be replaced by that 

 of a column of mercury. The branch or leaf-stalk, as the 

 case may be, is fixed air-tight into the short arm of a U 

 tube filled with water, and mercury is then poured into the 

 long arm until about 20 cm. pressure is obtained. The 

 whole is then covered with a bell-jar standing in water, 

 and after a time drops of fluid are found hanging to the 

 leaves. We found that with 25 cm. of mercury the drops 

 appear very rapidly on the leaves of the Balsam (Impatiens 

 halsamina). Moll also recommends Begonia and Phaseolus : 

 in the last named the fluid is, as Moll says, found on the 

 lower surface of the leaf. 



(91) Absolution by means of dead roots. 



Several observers^ have shown that transpiring plants 

 can absorb water from the soil even after the roots are 

 dead. We have confirmed the fact on pot-plants of 

 Helianthus tuber osus. A thermometer having been forced 

 into the earth, the flow^er-pot is immersed in water so 

 hot that the soil is kept at a temperature of 60° — 65° C. 

 for two hours. In spite of this violent treatment the 

 leaves remain turgescent for several days, whereas control- 

 plants, shaken out of their pots and freed from soil, rapidly 

 wither. 



1 Bot. Zeitung, 1880, p. 49. Eeferences are given to Sachs' Lehrlmch, 

 1874, p. 660, and de Bary, Bot. Zeitimg, 1869, p. 883, for similar results. 



2 Strasburger, LeitiingshaJmen, 1891, p. 849, where references to 

 earlier experiments are given. 



