INFLUENCE OF LIGHT UPON ACTION OF STOMATA 
Lloyd, on the other hand, used two methods of experimentation, of which 
one was more natural and satisfactory than the other. His early method 
involved the measurement of stomata in strips of epidermis torn from leaves 
and fixed in absolute alcohol. Although there are many evident advan- 
tages in this method, even its convenience was never sufficient to convince 
everyone that there was no change whatever in the stomata by the most 
deft stripping of the epidermis from the surface of a leaf and the dropping 
of the strip into absolute alcohol. These objections are all avoided, though 
others may be raised, by making direct observation and measurement of 
the stomata in position on the living leaf, still attached to the plant which 
bears it. By attaching a Soyka flask, filled with water or an aqueous solu- 
tion of suitable composition, to the under side of the stage of the microscope 
so that the light is cooled before it reaches the leaf to be examined, one may 
directly observe the condition and the changes in the position of the guard 
cells as the illumination changes. 
We used this latter one of Lloyd's methods, but only on hot days did it 
seem necessary to us to apply the cooling cell. Measurements of the sto- 
mata on the leaves of plants of wheat, oats, rye, and barley, growing out of 
doors or in pots in the greenhouse, were made by bending over a leaf and 
gently applying and fastening it to the stage of a horizontal or other micro- 
scope for a minute, or a minute and a half, during which time the part of 
the leaf in the field was subjected to observation. The measurements 
were made by eye-piece micrometer, and made and recorded as rapidly as 
possible, so that no injury to the leaf and no change in position of the guard 
cells followed the slight darkening under the microscope. Most of the 
readings were made by daylight; but the few night readings showed the 
stomata to be closed in darkness. Measurements were made from two or 
three leaves on each plant for each period of time, and the average mean was 
taken in plotting each point; for in a group of plants there would always be 
some variation in the amount of light received by each plant and each leaf, 
both as to the times at which the most light would reach them and as to 
the quantities to which each would be exposed. In choosing the parts to be 
examined care was taken to select those leaves and those parts of leaves 
which were most isolated and most subject to variation at the particular 
times of examination. When the illumination is fairly equal for all the 
plants and all the leaves in a pot or box of plants of the same species, the 
condition of all the stomata is similar. This is not the case when the ex- 
posure is not similar. In cases in which the plants and their leaves were 
not similarly exposed all around, the turning of the plants so that they were 
similarly exposed was followed by the corresponding changes in the guard 
cells. No attempt was made to secure a series of readings for the early 
morning hours, or after sunset, because we were concerned primarily with 
the behavior of the stomata in relation to natural light; and we believe that 
intense artificial light disturbs and perhaps interferes with the natural 
action of the guard cells. 
