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IOWA ACADEMY OF SCIENCE Vor. XXIX, 1922 
the cicatrice generally reacts differently from the uninjured cells. 
Especially marked is the positive reaction for lignin with phloro- 
glucin. Tests for cutin, and suberin gave less positive results in 
most cases. 
In contrast to the single epidermal layer found covering most 
leaves their cicatrices show a considerable thickness involving 
always more than one layer of cells and commonly several. The 
cicatrice itself, moreover, shows a general correlation with the 
structure and thickness of the leaf concerned. Disregarding the 
collapsed dead leaf cells the healing tissue often approximates 
one-third the thickness of the blade ; but observation, even with the 
limited number studied, shows wide variation with leaves of 
different habitats. 
The nearest approach to agreement seems to be between the 
width of cicatrice and depth of palisade layer. In many cases the 
actual thickness of the cicatrice is nearly the same as that of the 
palisade of the same leaf (figs. 1, 2, 4, 6). In leaves where the 
mesophyll shows less differentiation the cicatrice is simpler and 
relatively thin (figs. 3, 5). 
The thickness of the walls of the scar-tissue also shows general 
agreement with those of the epidermis. If there is a heavily 
cutinized epidermis the leaf is likely to develop a thicker walled 
cicatrice. It should be noted that in the latter such thickening 
is not limited to the outer walls of the cicatrice and is in no sense 
a reconstructed epidermis. Pittosporum (fig. 6) and Lonicera 
(fig. 2) present sharp contrast with Red Clover (fig. 4) or 
Bryophyllum (fig. 3). 
This seeming correlation in width between palisade and ci- 
catrice, and in character of walls between epidermis and cicatrice, 
might be expected on general grounds. A thick cicatrice with 
heavier walls would be demanded under conditions inducing much 
palisade and heavier epidermal walls. 
