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IOWA ACADEMY OF SCIENCE Voi.. XXVUE 1921 
in effect and the cut margins quickly heal. A large part of the 
blade may be removed at one time without disaster to the remain- 
ing portions. 
3. Leaves may get along very well without midrib if there is 
considerable width of blade on either side to provide for conduc- 
tion and mechanical support. 
4. Broader leaves succeed very well without their principal 
veins, or even with- major veins and midrib destroyed. 
5. Larger veins act as barriers to conduction across them. 
This may be due in these experiments to loss of water from their 
broken ends, or to difficulty in getting water through them trans- 
versely. 
6. A submarginal zone, free from larger veins, is prominent 
in many leaves and is efficient for conduction in all directions. 
7. In some leaves the submarginal zone has developed a vein 
parallel to the edge of the leaf which functions for lengthwise 
conduction and connection of parts of blade. 
8. Irregular wounds reveal a marked ability of the conductive 
tissues of the islet borders to adapt themselves to unusual de- 
mands both as to. amount and direction of conduction. 
9. . Badly mutilated leaves show unexpected strength of blade, 
apart from all larger veins, in meeting mechanical strain. 
10. The rectangular system of islet groups, bordered by larger 
veins, may be efficient in the uninjured leaf, but is not adapted to 
dealing successfully with modified conditions resulting from 
wounds. 
Department oe Botany 
University oe Iowa 
