246 Groom.—Remarks on the Oecology of Coniferae. 
(b) The Transpiration Current up the Coniferous Stem 
may be Rapid. 
In view of the rapid transpiration of the larch, and the consequently 
rapid flow of water along the tracheides of the leaf, and in view of the large 
number of leaves borne indirectly or directly on the slender twigs, it seemed 
to me probable that the transpiration current in the larch would be quite as 
rapid as in dicotylous trees ; and this anticipation was strengthened by the 
fact that the layer of sap-wood of the larch is unusually narrow. 
I therefore made experiments as to the rate of ascent of water by 
means of the ordinary eosin method, in shoots of Larix decidua , Pseudo- 
larix Kaempferi , Abies pectin ata, Pinus sylvestris, and Fagus sylvatica. 
The experiments were conducted in such a manner as to give maximum 
results. They were performed in July, 1909, on hot or warm, mainly sunny 
days, on which a breeze or wind was blowing : the shoots were exposed 
out of doors to the breeze, and in most cases to direct intense sunlight, 
or in a minority of cases to strong diffuse light. So far as possible the 
shoots were selected with a considerable head of foliage, either on a single 
axis, or on a branched axis which surmounted a considerable basal leafless 
portion of the stem ; thus the current of the solution at the base was not 
distributed over several stems but travelled up a single axis. The shoots 
were amputated from the tree in such a manner that the region of severance 
was under water at the time of severance. Yet care was taken to avoid 
extreme results due to 1 negative pressure ’, as before being tested with the 
eosin solution the detached shoots were kept (in some cases in a confined 
space in darkness) with their cut ends dipping in water for periods varying 
from 35 minutes up to more than 24 hours. The duration of these 
preparatory periods designed to do away with ‘ negative pressure ’ is recorded 
in the second vertical column of the succeeding tables. 
I was unprepared for the rapidity of ascent of the dye, so that in a number 
of cases, when measuring the height to which the eosin had ascended in the 
shoot, I made the first cut, and sometimes some of the subsequent cuts, too 
low down the stem. The result was that in these cases the transpiring 
leaves on the upper part of the shoot were still exercising their suctional 
power and drawing up the eosin solution. Consequently, the time during 
which the eosin was ascending the stem was considerably greater than that 
intervening between the moments of placing the shoot in the eosin and 
removing it from the eosin. At the time of performing the experiments, 
I unaccountably failed to appreciate the extent to which this would modify 
the results as regards rate of flow ; and I omitted to record the actual 
moment at which the highest point reached by the eosin was located, 
or whether, in making the first cut, I had made it above or below the highest 
