THE MOLECULAR FORCES IN PLANTS. 185 



1 See Wiesner, Sitzunrtsberichte d. Akad. d. IViss. zn Wien, 1879, Abth. 1, Bd. 

 79, Aprilheft, and the same, Bd. 98, p. 670. Sea also Lietzmarm, Flora, 1887, 

 Bd. 70, and Mangin, Ext rait des Ann. de la Science agrom>m.jrun<j. t etc. T. 1, 

 1888. 



2 See Sachs, Handbuch d. Expert me ntalphysiologie d. Pfianzen, 1865, p. 250. 



3 See especially Adler, Inaugural-Dissertation, Jena, 1892, and also Stras- 

 burger, Histologische Beitrilge, Jena, 1891, Heft 3, p. 510. 



4 See Sachs, Arbeiten d. botan. Instituts in Wiirzburg, Bd. 2, p. 324, and M. 

 Scheit, B.,tan. Z fining, 1884, p. 180. 



5 See Hohnel in Pringsheim's Jahrbiicher, Bd. 12, p. 72. 



G See Pfeffer, Handbuch der Pjlanzenphysiologie, Bd. 1, p. 109, and von 

 Hohnel, Jahrbiicher, Bd. 12, p. 99. In comparative researches on negative 

 pressure, far more attention must be paid than hitherto to the length and width 

 of the vessels, to possible variations in the width of a vessel at different points, 

 to the capillary resistance of the vessels, and other conditions. It would carry 

 us too far to take all these matters into consideration here. See also especially 

 Adler, Dissertation, Jena, 1892, p. 42. 



7 The conditions relating to the negative pressure of air in the vessels have 

 been especially investigated by voa Hohnel (Haberlaadt's Wissenschl.-praktische 

 Vntersuchungen anf dem Gebiete des Pjianzenbaues, Bd. 2, pp. 89 and 120), and 

 Sachs (Arbeiten d. botan. Inttituts in Wiirzburg, Bd. 2, p. 168). 



V. THE ABSORPTION OF WATER BY PLANTS. 



69. Absorption of Water from the Soil by the Roots. 



When the soil is more or less moist, the individual particles of 

 which it is composed are surrounded by coats of water. We may 

 picture them as surrounding the elements of the soil in concentric 

 layers, and it is clear that the particles of soil will retain more 

 energetically those molecules of water in direct contact with them 

 than those more remote. This is in fact the case, as the following 

 experiment teaches. We grow a bean plant in a flower pot in 

 good garden soil, and when the primordial leaves have attained 

 a considerable size, the plant is put in a place where it is screened 

 from direct sunlight and can only transpire feebly. From this 

 time we supply no more water to the soil, so that the plant 

 gradually withers. When it has become very limp, we take small 

 samples, a few grams in weight, from parts of the soil traversed 

 by numerous roots, and accurately determine the quantity of water 

 they contain by drying at 100 C. I found, in experiments not 

 made with Phaseolus certainly, but with Cucurbita, that the humous 

 garden soil employed, still contained, after the plant had withered, 

 more than 15 per cent, of water ; and we thus see that a part of 

 the water of the soil is held very firmly by its constituent particles. 



