WOUNDING OF FOUAGE EEAVES 
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regeneration though many leaves were critically examined by 
means of binocular microscope. No sections were made relative 
to this point in my study as such seemed unnecessary. Obvious- 
ly the maximum need of water conduction occurs immediately 
following the wounding and before there could be any possibility 
of regeneration of the conducting cells or tissues. Wounded 
leaves generally showed within a few hours (and usually within 
a couple of hours) the total area that was later to turn brown, 
if any death of tissues resulted from the wounds. All results 
indicated that badly wounded leaves passed the crisis, as far as 
water conduction was concerned, before any cicatrization or re- 
generation could possibly assist, and that, this crisis safely passed, 
no serious difficulty was likely to be encountered on this account. 
Naturally subsequent cicatrization would assist in conserving 
water and would lessen the danger of infection. 
Many experiments indicated that the larger veins, when inter- 
rupted, act as obstructions to the movement of water across them. 
Whenever a strip or peninsula of living blade was crossed by a 
section of a larger vein it suffered as compared with similar 
areas without such barriers. The difficulty may have been due 
in part to water loss from the cut ends of the large veins. On 
general grounds one would expect considerable leakage from the 
interrupted xylem strands, thus prolonging the traumatic water 
loss. Studies in progress show that it is very difficult for a wound- 
ed leaf to heal the cut end of a vein. These interrupted veins 
therefore probably caused water loss long after the margins of the 
wounded blade had been healed through cicatrization. 
The inefficiency of the Basswood type of leaf also deserves 
consideration. Its uniform failure to meet difficult conditions 
may be due to the ladder arrangement of its major venation. It 
has numerous relatively large cross veins which unite at frequent 
intervals the main parallel lateral veins, thus enclosing rectangular 
groups of islets. This arrangement, however efficient it may be 
for normal conditions, seemed unsatisfactory for handling con- 
duction under the modified demands of these experiments. 
SUMMARY 
1. The ordinary foliage leaf, of necessity a more or less deli- 
cate and unprotected structure, is so organized as to withstand 
serious wounds as well as losses of considerable amounts of 
tissue. 
2. Injuries to the blade between larger veins are always local 
