Report on the Ascent of Water in Trees. 631 
authority of Sachs 1 , who took up Unger’s view 2 that the transpiration 
current travels in the thickness of the walls as water of imbibition. 
Then followed the reaction against the imbibitionists — a reaction 
which has maintained its position up to the present time. Boehm, 
who had never adopted the imbibition theory, must have the credit of 
initiating this change ; his style was confused and his argument marred 
by many faults, but the reaction should in fairness be considered 
as a conversion to his views, as far as the path of the travelling water 
is concerned. Nevertheless, it was the work of others who principally 
forced the change on botanists — e. g. von Hohnel 3 , Elfving 4 , Russow 5 , 
R. Hartig 6 , Vesque 7 , Godlewski 8 , and others. 
II. The second question has a curious history, and one that is not 
particularly creditable to botanists generally. It has been characterized 
by loose reasoning, vagueness as to physical laws, and a general 
tendency to avoid the problem, and to scramble round it in a mist of 
vis a tergo, capillarity famin chains , osmosis , and barometric pressure. 
An exception to this accusation (to which I personally plead guilty) 
is to be found in Sachs’ imbibition theory, in which, at any rate, the 
barometric errors were avoided, though it has difficulties of its own, as 
Elfving has pointed out. 
But the most hopeful change in botanical speculation began with 
those naturalists who, concluding that no purely physical causes could 
account for the facts, invoked the help of the living elements in the 
wood. To Westermaier 9 and Godlewski 10 is due the credit of this 
notable advance, for whether future research uphold or destroy their 
conclusions, it claims our sympathy as a serious facing of the problem 
by an ingenious and rational hypothesis u . 
1 Physiol. Vegetale (French Trans.), 1868, p. 235, and more fully in the Lehrbuch. 
Sachs also partially entertained Quincke’s well-known suggestion of movement of 
a film of water on the surface of vessels. 
2 Sitz. k.k. Akad. Wien, 1868. Dixon and Joly’s paper in the Annals of Botany, 
September, 1895, gives evidence in favour of a certain amount of movement of the 
imbibed water. 3 Pringsheim’s Jahrb., xii, 1879. 
4 Bot. Zeitung, 1882. 5 Bot. Centr., xiii, 1883. 
6 ‘ Ueber die Vertheilung,’ &c., Untersuchungen aus dem Forst. Bot. Inst, zu 
Miinchen, ii and iii. 
7 Ann. Sc. Nat., xv. p. 5, 1883. 8 Pringsheim’s Jahrb., xv, 1884. 
9 Deutsch. Bot. Ges., Bd. i, 1883, p. 371. 10 Pringsheim’s Jahrb., xv, 1884. 
11 It is of interest to note that Hales, in speaking of the pressure which he found 
to exist in bleeding trees, says : ‘ This force is not from the root only, but must also 
proceed from some power in the stem and branches.’ Veg. Staticks, 1727, p. no. 
