METHODS. 



conditions which conceivably might affect the size of the stomatal openings, 

 there are no reasons to believe that stripping the epidermis leads to perma- 

 nent distortion or change in dimensions. That a local temporary distortion 

 occurs during the stripping is certain, but this has no more permanent effect 

 than pressure on a rubber ball, upon the release of which it reassumes its 

 rotundity. I have satisfied myself by direct observation that this holds true 

 in Fouquieria splendens and Verbena ciliata, and on this point I am in full 

 agreement with Czeck (1869). Thus, when a piece of epidermis is removed, 

 there is frequently an unharmed portion of the leaf taken with it. If properly 

 observed, the stomata on the unharmed area will accord in size with those in 

 the free epidermis. But if mounted in water, differences may be seen, due not 

 to the release of tensions, but to the access of water into the guard-cells. 



Another form of the objection that tearing off the epidermis produces 

 mechanical disturbances has been urged by Kohl (1885). He found that, on 

 placing epidermis in water, the stomata which were placed near and with 



FIG. 7. Stoma of Verbena ciliata, from epidermis torn 

 from leaf and examined in water. The torn edge 

 is above. 



FIG. 8. Stomata of Verbena ciliata, in epider- 

 mis torn from leaf and fixed in absolute 

 alcohol. 



their major axes parallel to the edge of the removed piece of epidermis had 

 larger openings than those removed some distance from the edge or had their 

 major axes perpendicular to it (cf. his plate i, fig. 4) . Such changes of form 

 might conceivably occur as the result of released pressures near the margin 

 of a torn piece of epidermis. If this were true it might be taken as evidence 

 of the mechanical effect of adjoining epidermal cells upon the form of the 

 stomata, as Kohl indeed holds. But I have not found that, either in ocotillo 

 or Verbena, the form of stomata in such position is changed, for I have 

 repeatedly observed, as is exemplified in figs. 7 and 8, that the shape of 

 the stomata and the sizes of their openings are not changed in any way by the 

 tearing or by the resulting setting free of tensions, for, when pieces of epidermis 

 are at once fixed in absolute alcohol, the stomata are as uniform as to the size 

 of their openings and as to their form along the edge of the piece as elsewhere. 



