294 
IOWA ACADEMY OF SCIENCE You XXVIII, 1921 
With such diveerse conditions even in different parts of the same 
plant it was not thought best in this series to try to evaluate the 
degrees of difference. So, while note was taken of the differences 
between interior and exterior leaves of given plants as well as the 
contrasts between sun and shade leaves of the same tree, there 
was no attempt in this connection to get other than qualitative 
results. 
The wounding of the leaves was carried out in part by means 
of a leather-punch with cutting margin of the shell thinned down 
and sharpened to a keen edge, and having base covered with a 
rubber pad. With this tool, which removed a circle of tissue 
3 mm. in diameter, it was possible to excise any desired portions 
of a leaf or to cut out cleanly a section of a vein and its bor- 
dering blade (Figs. 49-52). Moreover, the cut edges were left 
so far apart that they were fully exposed to dessication and in- 
fection, thus simulating the conditions resulting from natural 
wounds due to leaf eating larvae, etc. 
In another series of experiments (Figs. 53, 54) slits were cut in 
leaves by means of a large razor, the leaf meanwhile being sup- 
ported underneath by a sheet of heavy cardboard. While this 
left a smooth straight margin, the wounded edges, especially at 
the ends of the slits, were somewhat mutually protective. 
Studies by the writer, as yet unpublished, outline the methods 
on the part of foliar organs by which they repair their wounded 
margins. These studies show that cicatrization of foliar wounds 
is slow in starting but is well advanced within ten days and that 
traumatic, water loss, very severe at first, probably ceases in half 
that time. With these earlier results in mind the experiments 
with which this paper deals were in some cases shortened as 
much as possible. This knowledge, for instance, enabled one to 
leave mechanically weakened leaves a minimum time, thus lessen- 
ing the danger of destruction from winds. Since the primary 
object sought was to determine the conductive efficiency of minor 
veins, there was no gain from further prolonging the experiment 
after such results were obtained. It was a matter of surprise, 
though, to see how successfully many badly wounded leaves sus- 
tained themselves mechanically though lacking seemingly funda- 
mental parts. 
While numerous variations of methods of wounding were tried, 
singly or in combination, those here discussed might be sum- 
marized as follows: 
(1) Destruction of the midrib in one or more places. (2) 
