ee Si 
gy IO ¢ 
ON THE ASCENT OF WATER IN TREES. 677 
part which may still be effective. He also doubts ‘whether the cells were 
always killed at once.’ The first objection of Schwendener’s may or may 
not be sound, but in any case it does not (as Strasburger points out) ac- 
count for the experiment! in which an oak stem was poisoned by picric 
acid, and three days afterwards was placed in fuchsin-picric. The second 
reagent had to travel in tissues already killed with picric acid, yet a height 
of 22 m. was reached. 
The question whether the reagents kill the cells in Strasburger’s 
experiments does not lend itself to discussion. It is difficult to see how 
they should escape, and we have Strasburger’s direct statement that the 
living tissues were visibly killed. It must not be forgotten that in some 
of his experiments the death of the tissues was produced by prolonged 
boiling, not by poisons.?, Thus the lower 12 m. of a Wistaria stem were 
killed in this way, yet liquid was sucked up toa height of 108 cm. In 
the Histolog. Beitr., v. p. 64, he has repeated his air-pump experiment, 
using a boiled yew branch, and found that eosin was sucked up from a 
vessel in which almost complete vacuum was established, so the action of 
living elements and of atmospheric pressure was excluded. 
On the whole, the balance of evidence is, in my judgment, against the 
belief that the living elements are necessary for the rise of water. In 
other words, I think we should be justified, from Strasburger’s work, in 
seeking the cause of ascent in the action of purely physical laws. 
Strasburger’s general argument from the structure of wood.—lt seems 
sometimes to be forgotten that, apart from the physiological or experi- 
mental evidence, there is another line of argument founded on the 
structure of wood. Strasburger’s unrivalled knowledge allows him to use 
this argument with authority, and he seems to me to use it with effect. 
Thus? 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 difficulties. This is, he says, 
especially the case in Dracena. He goes on to point to difficulties in the 
case of such dicotyledons as Albizzia. The case may perhaps best be put 
in the generalised manner that Strasburger himself employs.* If the 
living elements are of such importance as Godlewski, Westermaier, and 
Schwendener hold, we ought not to find these difticulties; 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 remem- 
bered 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 Joly and of Askenasy.—I now pass on to the 
recent work in which Strasburger’s indications to search along a purely 
physical line have been followed ; namely, the paper of Dixon and Joly,” 
1 Hist. Beitr. v. p. 12. 
2 Leitungsbahnen, p. 646. 
8 Hist. Beitr. v. p. 17. 
4 Loc. cit. p. 20. 
5 Proc. Roy. Soc., vol, lvii. No. 340. Also Annals of Bot., vol. viii.; Phil. Trans., 
vol. 186, 1895 (B). 
