Transpiring Branches . 441 
a maximum tension of 23! in. : on the morning of July 4, 
leafy twigs were removed from it so as to reduce its leaf-area 
by at least two thirds, and it then gave (July 4-5) a maximum 
tension of 23 in. On the removal of the whole of its leaves, 
the tension (July 5-6) reached i8J in. 
However, these figures also show that in certain cases the 
reduction of the leaf-area did materially lower the maximum 
tension and prolong the time required to attain it, though not 
to the extent that might have been expected. The leaf-area 
is, then, a factor in determining the maximum tension attain- 
able by a shoot, but it is not the only factor ; what the 
other factors may be has yet to be ascertained. It seems to 
me probable that one other factor is the antecedent condition 
of the shoot. When the transpiration of a shoot, previously 
to an experiment, has been greater than its absorption of 
water, a considerable tension is set up within it ; this tension 
appears to persist as an after-effect, and to enable the shoot 
to develop a high tension in a subsequent experiment, even 
though its leaf-area is largely diminished. This is the only 
way in which I am able to account for some of the observa- 
tions tabulated on the previous page. The remarkable 
behaviour of the leafless stem of Helianthus , I attribute in 
part to the fact that the stem is itself an efficient organ of 
transpiration. 
I come now to another enquiry, the enquiry, namely, as to 
the relation between the life of the shoot and its suction-force. 
I have not been able to make many observations in this 
direction, but such as they are, they give some indications. 
A branch of Beech (B) with 344 leaves gave (June 25) 
a maximum tension of i8^in. It was left all night with io°/ o 
solution of copper sulphate (CuS 0 4 ) being injected into it 
by a 3 ft. siphon : on the following morning, drops of the 
copper-solution were exuding from wounds where small 
branches had been cut off, but the leaves still looked fresh 
and green: that day a maximum tension of 14! in. was 
attained, and, after being left all night, the tension indicated 
next morning (June 27) was 14^ in., the fall being due to an 
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