VENATION OF FOLIAGE LEAVES 
237 
was removed with scissors before the leaf was slashed longitudi- 
nally with razor, so as to equalize water loss for all strips. Re- 
calling the marked efficiency shown by the leaf of Lilac in earlier 
experiments (1. c., p. 301) conditions for these sun leaves were 
made doubly difficult by continuing the slashes through the end 
of the leaf thus reducing the blade to a series of strips with con- 
nection only at the base. The shade leaf (fig. 1, a) suffered no 
loss of tissue though the slits were long and the strips of tissue 
quite narrow. Of the sun leaves the one with broader strips (c) 
suffered no loss of tissue and the other (b) with much narrower 
zones lost only a little in three or four places. 
Comparisons are difficult in the absence of precise environmental 
data together with facts relative to amount of water loss, etc. 
But assuming, roughly, proportional loss from wounds and trans- 
piration and like efficiency of stem for raising water, etc., the 
type of venation seems to be an important factor in wound toler- 
ance. 
The development of a submarginal system, unless this is inter- 
rupted, adds greatly to the leaf’s conductive efficiency. In 
Asclepias syriaca there is an evident transverse-longitudinal or- 
ganization, the latter represented by the midvein and lateral sub- 
marginals. Wounding experiments indicate that this plan is in- 
elastic though doubtless efficient in the normal leaf. In Lilac the 
oblique laterals, in combination with a marginal plexus of smaller 
veins, seem to constitute a versatile arrangement very useful in 
meeting conditions demanding modified flow of materials. It 
would appear that in the outer part of the leaf a plexus of con- 
necting veins offers advantage over a definite, single submarginal 
vein. 
Department oe Botany, 
University oe Iowa. 
