PHYTO-PHYSIOLOGY. 271 



thus the vegetable sap is attracted by the root and 

 by the stalk. But the differencing or the oxygen pole is 

 the stronger of the two. The determining principle of 

 the movement of the sap resides consequently in the 

 stalk, and the chief direction of the sap-motion tends 

 upwards. 



1445. At times, when the air-polarity is elevated, the 

 sap also ascends more rapidly. As in summer, upon 

 clear warm days. It ascends slowly upon gloomy and chill 

 days. That in this also light and heat are playing their 

 parts, is self-intelligible. Thereby the upper particles of 

 sap become lighter and ascend, being pressed upwards 

 by the lower and colder particles. As they are never- 

 theless by no means changed, this is a proof that, during 

 the time so employed, polar forces also act upon them. 



1446. But the root has also the endeavour to attract 

 the sap ; but as its pole is feebler in character, the 

 stalk draws the sap from the ultimate extremities of 

 the " root into itself. If accordingly the polarity of the 

 air becomes weaker, while the plant is losing its leaves 

 or the organs of polarization ; so is it easy to imagine 

 why the motion of the sap becomes slower. As, however, 

 the aerial polarity is always stronger than that of the 

 earth, the sap must thus in winter also take the same, 

 or upward, direction. 



1447. A fall or descent of the sap can therefore never 

 take place abstractedly forsooth from the root, in which 

 it sinks by its own gravity. How a part of a plant, e. g. 

 a twig, could continue alive, were the sap to have fallen 

 or receded from it, is not to be conceived. It does not 

 follow from what has been just stated, that movements 

 of sap should not take place in all directions, and con- 

 sequently too downwards ; they must indeed occur ra- 

 ther than otherwise, and that indeed upon all sides ; only 

 the principal track or course of the sap must always 

 pass in the direction upwards. 



1448. The movement of the sap consists simply in an 

 ascent and impulsion of its particles upon all sides, but 

 without any circulation. A circulation would only be 



