655 
the Ascent of Water in Trees. 
intervals of time and at different pressures, of the weight of a small 
phial of water surrounding the cut stem of a branch which, previous 
to experiment, has been left standing for some time in water. 
The pressure first giving rise to the ejection of water under these 
circumstances assigns a limit to the functioning of the cell as one 
holding the maximum quantity of water which its voluminar distension 
admits. 
The second phenomenon is observed directly in the curling up of 
the leaves, which roll slowly inwards from the edges and simultaneously 
droop upon the petiole. By relieving the pressure the leaf will in 
many cases recover its original form in the course of a few minutes. 
It may, in fact, be caused to curl up slowly and open out repeatedly 
like a Bourdon tube. The pressure giving rise to crumpling is that 
which assigns a limit to the ultimate tractive force of the cell and 
to its functioning as a healthy organ. 
A striking fact is revealed in the course of these experiments : — 
The use of carbon dioxide as the agent for producing the pressure 
gives a markedly lower result than the use of air. In fact the limits 
of resistance fall to about one-third or one-fourth of their value. 
In the case of Cytisus Laburnum a pressure of between 6 and 
8 atmospheres of carbon dioxide will cause the crumpling of the 
older leaves, although the younger ones will still remain turgescent : in 
fact 1 6 atmospheres of carbon dioxide were attained without crumpling 
of the younger leaves being observed. First at 26-6 atmospheres of 
air the older leaves of Cytisus began to curl up. At 20 atmospheres 
of air the saturation limit of the osmotic force was reached. 
In the case of Tilia americana a pressure of between 7 and 8 
atmospheres of carbon dioxide gave slight collapse, while, according to 
Dixon’s most recent experiments, a pressure of 20 atmospheres of air 
did not produce collapse. The saturation limit for this tree was 
reached, when carbon dioxide was used, at 4 atmospheres. With 
the use of air it was reached at 15 atmospheres upon a branch 
which had been already experimented with. A prior observation 
upon this branch gave no loss of water at 15 atmospheres of air. 
In the case of Helianthus multiflorus 20 atmospheres of air produced 
collapse, the rolling up and flagging of the leaf being beautifully 
marked. At 13 atmospheres it held out. The osmotic limit of resist- 
ance may therefore be taken between 13 and 20 atmospheres in 
this plant. 
