635 
the Ascent of Water in Trees. 
use this argument with authority, and he seems to me to use it with 
effect. Thus 1 he points out that though in coniferous wood the 
action of the living elements in pumping water is conceivable, yet this 
is far from being universally the case. He points out that in the 
Monocotyledons such theories meet with almost unconquerable diffi- 
culties. This is, he says, especially the case in Dracaena. He goes 
on to point to difficulties in the case of such Dicotyledons as Albizzia. 
The case may perhaps best be put in the generalized manner that 
Strasburger himself employs 2 . If the living elements are of such 
importance as Godlewski, Westermaier, and Schwendener hold, we 
ought not to find these difficulties ; we ought rather to find structural 
peculiarities pointing distinctly to the existence of such functions. For 
instance, we ought to find the tracheal water-path actually interrupted 
by living elements, which might act like a series of pumping stations 
one above the other. It should, however, be remembered that if we 
deny the importance of the medullary rays and other living elements 
in raising water, we ought to be able to point more clearly than we can 
at present to the function of the medullary rays and to structural 
adaptations to these functions. 
The work of Dixon and Joky and that of Askenasy. — I now pass on 
to recent papers in which Strasburger’s indications to search along 
a purely physical line have been followed. In 1894 Messrs. Dixon 
and Joly 3 first enunciated an entirely new theory, depending upon the 
quality which water possesses of resisting tensile stress. To most 
botanists the existence of this quality is a new idea. To believe 
that columns of water should hang in the tracheals like solid bodies, 
and should, like them, transmit downwards the pull exerted on them 
at their upper ends by the transpiring leaves, is to some of us equivalent 
to believing in ropes of sand. Meanwhile Askenasy had independently 
hit on a similar theory which was published 4 after the appearance of 
Messrs. Dixon and Joly’s research. 
Askenasy has earned the gratitude of his botanical readers by giving 
some of the evidence which demonstrates the existence of this property 
of water 5 . A tube a metre in length was filled by Donny with water, 
1 Hist. Beitr. v. p. 17. 2 Loc. cit., p. 20. 
3 Proc. Roy. Soc., Vol. lvii, No. 340 (1894). Also Annals of Bot., Vol. viii ; Phil. 
Trans., Vol. 186, 1895 (B). 
4 Verhand. a. d. naturhist. med. Vereins Heidelberg, N. F., Bd. v, 1895; and 
N. F., Bd. v, 1896. 
5 He gives references to Donny, Poggendorffs Annalen, 67. Bd. (143. Bd. d. g. R.) 
U U 2 
