5 a at NR OM _ 
ON THE ASCENT OF WATER IN TREES. 675 
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 & tergo, 
capillarity, Jamin 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 baro- 
metric 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 ' and Godlewski ? 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.? 
We may pass over the cloud which arose to witness for and against 
these theories, and proceed at once to Strasburger’s great work,‘ in which, 
with wonderful courage and with the industry of genius, he set himself 
to work out the problem de novo, both anatomically and physiologically. 
In my opinion it is difficult to praise too highly this great effort of 
Strasburger’s. 
Strasburger’s general conclusion is now well known. He convinced 
himself that liquid can be raised to heights greater than that of the 
barometric column in cut stems, in which the living elements have been 
killed. Therefore, the cause of the rise could not be (1) barometric 
pressure, (2) nor root pressure, (3) nor could it be due to the action of 
the living elements of the wood. His conclusions may be stated as 
follows :— 
(a) The escent of water is not dependent on living elements, but is a 
purely physical phenomenon. 
(5) None of the physical explanations hitherto made are sufficient to 
account for the facts. 
Strasburger has been most unjustly depreciated, because his book ends 
in this confession of ignorance. I do not share such a view. I think to 
establish such distinct, though negative, conclusions would be, in this 
most nebulous of subjects, an advance of great value. Whether he has 
established these conclusions must of course be a matter of opinion. To 
discuss them both would be to go over 500 pages of Strasburger’s book, and 
will not here be attempted. Conclusion (a) that the ascent is not de- 
pendent on living elements must, however briefly, be discussed, because it 
is here that the roads divide. If we agree with Strasburger, we know 
that we must seek along the physical line ; if we differ from him, we are 
bound to seek for the missing evidence of the action of the living 
elements. 
Schwendener’s Criticism.—Perhaps the best plan will be to consider 
the most serious criticism that has been published of Strasburger’s 
work, namely, Schwendener’s paper ‘ Zur Kritik,’ &c.? 
! Deutsch Bot. Ges., BA. i. 1883, peor. 
2 Pringsheims Jahrb., xv. 1884. 
* 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. 110). 
+ Leitungshahnen, 1891. 
* K. Preuss. Ahad. 1892, p. 911, 
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