SOME WOUND RESPONSES OF FOLIAGE LEAVES 
ROBERT B. WYRIE 
The leaves of plants are their most exposed organs. The thin 
summer foliage of herbaceous plants and deciduous trees gen- 
erally suffers so severely that one rarely finds an uninjured leaf. 
While the degree of wounding is less serious in the evergreens, 
since they are tougher and offer greater resistance, lesions are not 
uncommon on these especially on the broader leaved evergreens. 
The plant’s ability, therefore, to deal with such frequent accidents 
must be highly developed to meet these daily needs for renewed 
cortex. 
Recalling that the leaf is usually an organ of definite growth, 
its tissues quickly passing into functional maturity, and that 
wounds expose many layers of living cells remote from all grow- 
ing tissues, the writer has often remarked the apparent efficiency 
of the leaf in dealing with its wounds. Infections through lesions 
in leaf tissue seem relatively unimportant in relation to plant 
diseases while wounds on stems commonly contribute to the 
liability of infection. Leaf wounds though most numerous of 
all types of lesion in plant tissues apparently have relatively the 
least to do with plant diseases. 
While leaves have been studied intensively from many view- 
points their normal tissue responses to traumatic stimuli have 
received relatively little attention from botanists. This is in 
itself proof of the marked efficiency of the leaf to take care of its 
wounds. When galls are produced such have invited special 
investigation and their literature is extensive. Very few papers, 
however, discuss the morphological changes in consequence of 
lesions in a foliage leaf unless followed by abnormal growths. 
Since no paper at hand seems to bear directly on these morpho- 
logical responses it seems best to defer the discussion of all papers 
that might find a place in the summary of literature to a later 
paper in which the writer traces the development of the cicatrice 
in certain leaves. 
The work of the foliage leaf compels a structure that invites 
animal attack and also renders the leaf liable to mechanical 
injury. Photosynthesis is possible only as light enters the leaf, 
