641 
the Ascent of Water in Trees. 
quantity in four-year-old wood. In the same month Pinus Salzmanni 
(Laricio) showed scattered bubbles in the spring wood of last year, and 
more in the autumn wood. In a Larch there were only very occasional 
bubbles in the two last years’ wood. In the Silver Fir the current year’s 
wood was practically free from air : the air increased in the inner 
rings. Tsuga canadensis had no air in this year’s wood, only a little 
in last year's* and an increasing quantity in the older rings, the fifth 
being very rich in air. In February, Pinus Strobus had hardly any air 
in this year’s wood, and the Silver Fir was all but free from it in the 
youngest ring. Robinia in July had the youngest wood almost air-free. 
Ficus elasiica and spuria , various Acacias , and willows gave vessels 
not entirely free from air, but nearly so. He concludes 1 that the 
path of the transpiration-current is not absolutely free from air. The 
younger wood, which especially functions as the water-carrier, is the 
most free. 
Dixon and Joly quote Strasburger’s results, which they consider 
sufficiently favourable to their views. They rely, in addition, on the 
impermeability of wet cell-walls to air isolating the conduits in which 
air has appeared ; and on the possibility that the air may be redissolved 
under root pressure 2 , an idea well worth testing. 
I think Strasburger’s facts are not so favourable to their theory as 
these authors believe ; in the same way it seems to me that Askenasy is 
rash in saying 3 that the tracheals in many cases contain continuous 
columns of water. It is true that this statement does not affect the 
validity of his general argument, since he faces the undoubted occur- 
rence of air bubbles in many cases. This is undoubtedly necessary, 
and fortunately we can once more turn to the Leitungsbahnen. Stras- 
burger states that he has seen water creep past the air-bubbles 4 in 
coniferous tracheids. The best evidence for this seems to be the fact 
mentioned 5 that the part of a single tracheid in front of an air bubble 
gets red with absorbed eosin, though the neighbouring tracheids are 
colourless. This clearly suggests the creeping round the bubble which 
Strasburger believes in. Schwendener 6 has been unable to confirm 
Strasburger’s microscopic observations, and moreover denies the 
physical possibility of the phenomena. I am unable to judge of the 
1 Loc. cit., p. 688. 2 Phil. Trans., p. 572. 
3 Verhand. naturhist. med. Vereins Heidelberg, 1895, p. 15. 
* Leitungsbahnen, pp. 704, 709. See also Hist. Beitr. v. p. 76. 
5 Ibid., p. 79. 6 Zur Kritik, &c., p. 921. 
