1gtt] OV ERTON—TRANSPIRATION AND SAP-FLOW 41 
of the leaf is usually very rapidly lost when dead, after which the 
amount decreases more uniformly. 
' Jost puts the question clearly in maintaining that ‘‘a completely 
convincing experiment must show that the leaves which are supplied 
with water by a dead stem are able to remain for a long time alive.”’ 
The difficulty so far has been, in part at least, to render the living 
cells of a stem inactive without causing other changes, or only such 
as may beignored. It has been observed by BoEHM (3) and StrRas- 
BURGER (30), among others, that in experiments in which certain 
portions of a stem are killed with steam, the leaves above these 
regions wither and die sooner than in the control, a phenomenon 
which KosaArorFr (20, 21) also observed in his experiments on 
cooled stems. That water passes through the scalded or cooled 
region has been shown many times by placing cut ends of the stems 
in dyes. That it does not pass in sufficient quantities may perhaps 
be the cause of the earlier withering of the leaves on a branch, a 
section of which has been killed, as has been urged by URSPRUNG, 
Ewart, and by RosHarpt in support of the vitalistic theory of 
sap-flow. Ursprunc employed steam and low temperature to 
kill sections of the stem in certain woody plants, or removed the 
bark without otherwise disturbing the connection between root and 
stem. In addition to steam, RosHARDT has used low temperature, 
and in certain cases xylol or ether. According to these authors, 
earlier withering of the leaves is a sure sign that a sufficient water 
supply does not pass through the killed portion. Both authors 
have shown that the longer the killed portion is, the more quickly 
the leaves above wither and fade, as was formerly observed by 
JANSE (16). we 
That SCHWENDENER (29) still adheres to the vitalistic hypothe- 
sis of sap-flow is shown by certain passages in the last edition of 
his lectures on mechanical problems in botany, in which he says: 
Ohne dieses Eingreifen (Lebensthitigkeit der Zellen) ist die Hebung 
des Wassers auf Héhen von 150-200 Fuss und dariiber einfach unméglich und 
alle Bemithungen, die vorhandenen Schranken mit unklaren physischen An- 
nahmen zu durchbrechen, sind nicht viel mehr als ein Suchen nach dem Stein 
_ der Weisen. 
LECLERC pU SABLON (22) believes that the ascent of sap is 
easily explained by the osmotic qualities of the living cells of the 
Se Sa Peis 
