IY ang 
II. 
NOTE ON THE SUPPLY OF WATER TO LEAVES ON 
A DEAD BRANCH. 
By HENRY H. DIXON, Sc.D., 
Professor of Botany, Dublin University. 
[ Read, June 20 ; Received for Publication, June 23 ; Published, Ave. 1, 1905.] 
Ursprune, in a paper appearing in the “ Beihefte zum Botani- 
schen Centralblatt,’’ discusses the possibility of the participation 
of the living cells of the stem in the elevation of the transpiration 
current. He considers it d priori conceivable that these cells may 
enter into the process in two different ways—(1) by directly 
elevating the water, or by partially supporting the hydrostatic — 
head ; and (2) by keeping the vessels and tracheids in a condition 
suitable for transmitting water. 
With regard to the first assumed possibility, it may be observed, 
as has been pointed out, that no process taking place in the cells 
adjoining the water-conduits can be effective in raising the water 
through these conduits as long as water is free to move equally 
readily up or down in the conduits. Experiments seem to have 
abundantly proved the absence of valves or other unidirectional 
_ structures in the water-tracts of plants. Hence, judging from the 
known physical properties of the water-conducting tissues and the 
relation of the living cells of the stem to them, there is no 4 priort 
reason for supposing that these latter are effective in raising water 
to levels above themselves during transpiration. Rather all that 
we know is opposed to such a supposition. 
Ursprung, however, seeks to demonstrate this function for the 
living cells by direct experiment. He quotes, in the first instance, 
Strasburger’s experiments, in which great lengths of stems were 
killed by immersion in hot water, and, according to him, the result, 
viz. the withering of the leaves above the killed portions, although 
1 Band xyiii., Abt. I., Heft 1, 1904. 
SCIENT. PROC. R.D.S., VOL. XI., NO. II. 
