( 563 ) 
Botany. — “Sap-raising forces in living wood” By E. Reinders. 
(Communicated by Prof. J. W. Moll.). 
Of the many theories, which have been advanced in explanation of the 
transpiration-current of trees, most are at present only of historical impor¬ 
tance in the literature. The imbibition theory of Sachs 1 ) ; Bohm’s atmos¬ 
pheric pressure theory 2 ); the gas pressure theory of Hartig *); the views 
of Westermaier 4 ), who regarded the xylem parenchyma as the water 
conduit and considered the vessels to be reservoirs; Ewart s *) hypo¬ 
thesis that the living elements help te overcome the resistance, the 
cohesion theory of Askenasy ®), which neglected to adopt the conti¬ 
nuity of water as a conditio sine qua non — all these have been 
given up. On the other hand opinion is still divided with regard to 
two hypotheses, the advocates of which combat the views of their 
respective opponents with remarkable asperity. Godlewski 7 ) and his 
supporters defend the view that the transpiration-current cannot be 
explained without postulating the cooperation of the living elements 
of the wood • Dixon and Jolt 8 ) on the other hand advance the 
proposition that the living elements have not, and cannot have, 
anything to do with the process. They explain the phenomenon that 
water ascends up to the summits of the highest trees by assuming 
that in these trees the water, enclosed in the narrow water conduits, 
hangs like a thread from the surface of the leaf cells, where it is 
held by capillary or other physical forces. The thread does not break, 
because, as is supposed, it is nowhere in contact with air, and in 
these circumstances water can support a tension of 150 atmospheres. 
When the water evaporates in the leaves at the summit, this thread 
is drawn up through the tissues. . 
The keenness with which the two parties oppose each other is 
best illustrated by a couple of quotations. 
Schwendener 9 ), an advocate of the more physiological theory, 
“An der Vorstellung, dass die Lebenstatigkeit der Zellen irgendwie 
in die Saftbewegung eingreift isi . . . . unbedingt festzuhalten. Ohne 
dieses Eingreifen ist die Hebung des Wassers auf Hohen van 150-200 
Fuss und dariiber einfach unmoglich ' und alle Bemiihungen, die vor- 
‘handenen Schranken mit unklaren physischen Annahmen zu durch- 
brechen, sind nicht viel mehr als ein Suchen nach dem Stem der 
Weisen”. 
In the same year 1909 Dixon 10 ) writes 
“The adhesion of writers to the vital hypothesis .... is so 
Proceedings Royal Acad. Amsterdam. Vol. Xil. 
