23 o THE MOVEMENTS OF WATER 



Direct experiments by Vesque, Kohl, Eberdt, and Kosaroff ' have shown 

 that the absorption of water by roots, and also by cut stems, diminishes as 

 the temperature falls. Nevertheless a perceptible absorption of water may 

 still occur at or even below zero. Thus Kosaroflf found that a flaccid plant 

 might absorb sufficient water from soil frozen at 3 to 4C. to become 

 turgid again in air saturated with water vapour, or even to counterpoise 

 feeble transpiration. This is of course possible only in plants whose roots 

 are not injured by such exposure (Chelidonium, Sinapis, Chrysanthemum 

 indiaim}. At 3 to 4 C. the whole of the water present in the soil or 

 in the plant is not frozen, so that from a purely physical point of view it 

 is easy to understand that a root of Salix or Chrysanthemum may absorb 

 water at 3 C. or 4 C. from a block of ice into which it is frozen. 



A low temperature retards the passage of water through the living 

 root-cells and vascular tissue. This is a necessary physical consequence 

 of the low temperature ~ ; indeed in the vascular tissue it appears to be 

 due to physical causes alone, for it has been observed that a transpiring 

 plant of Passiflora cocntlca or of Lonicera sempervirens, whose roots were 

 kept in moist soil at 15 C. to 20 C., remained turgid, although the stem 

 was cooled to o C. for a length of 70 cm. 3 , but became flaccid when the 

 temperature of the stem was lowered to i\5C. to 3 C. Dixon and 

 Joly 4 , however, have observed a slight movement of water in tracheae at 

 a temperature of 5 C. 



The vital activity of the intermediary cortical and epidermal cells 

 appears to be of importance in the transference of water to the tracheal 

 channels. This is indicated by the disproportionate influence exerted by 

 temperatures approaching or falling beneath zero, but more conclusive 

 evidence is afforded by the fact that the presence of a high percentage of 

 carbon dioxide in the gases of the soil or in a culture fluid causes a diminution 

 in the rate of absorption, while if the surrounding oxygen be replaced by 

 a neutral gas a similar but less marked result is produced 6 . The same 

 agencies will cause a slowing or cessation of bleeding, and the changes 

 induced in both cases are somewhat closely related. 



Evergreens transpire much less actively in winter, partly because the 



1 Vesque, Ann. d. sci. nat., 1876, vi. se>., T. IV, p. 89, and 1878, vi. sen, T. vi, p. 169; 

 Kohl, Transp. d. Pflanzen, 1886, p. 63; Eberdt, ibid., 1889, p. 61 ; Kosaroff, Einfluss versch. 

 Factoren auf d. Wasseraufnahme, Leipziger Dissertation, 1897. 



4 According to Dimitrievicz (Haberlandt's wiss. prakt. Unters., 1875, Bd. I, p. 75) and Reinke 

 (Hanstein, Bot. Abhandlungen, 1879, Bd. IV, p. 83), the swelling of seeds takes place more slowly 

 at a low temperature. Detmer's experiments upon the rapidity with which wood absorbs water at 

 different temperatures are less conclusive (Beitrage zur Theorie d. Wurzeldrucks, 1877, P- 3^)- 



8 Kosaroff, 1. c. 



4 Dixon and Joly, Annals of Botany, 1895, Vol. IX, p. 416. 



Kosaroff, I.e. W. Wolff (Jahresb. d. Agriculturchemie, 1870-2, p. 134) found the passage 

 of a stream of carbonic acid gas through a nutrient solution acted in a similar manner. 



