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IOWA ACADEMY OF SCIENCE Vox.. XXVIII, 1921 
Fig. 52. Feaves with U-shaped cuts thus making unusual demands on the blade- 
tissue both as to amount and direction of flow. 
of conduction in different parts of the blade as well as in different 
directions a series of U-cuts was arranged which yielded some 
surprising results. In preparing these experiments the leaf-punch 
was used which cut out a broad zone of blade around the penin- 
sulas of living tissues, thus exposing their freshly wounded mar- 
gins to the fullest effects of evaporation. In earlier attempts 
the projecting lobe of the blade was given mechanical support 
by lacing across the gap with a few stitches of fine thread (i) thus 
tying the lobe to adjacent portions of the blade and holding the 
peninsula in position. But it was soon found that such precau- 
tion was unnecessary so in all subsequent cases the lobe was left 
without artificial support, which greatly simplified the procedure. 
The U-cuts were tried on all leaves of the series except the milk- 
weed. There was considerable variation in position, direction, 
and form, some having the open end of the U constricted by 
curving inward the arms on either side (h). 
In some cases midribs or larger veins were left as leaders into 
the peninsulas, either directly (a), or inversely in the instances 
of inverted U-cuts (a, e, f). In others no large vein was left as 
