4 Lioyp: LEAF WATER IN GOSSYPIUM 
shape of the microscope,* but these limitations are not as strait 
as one might suppose. For the direct visual observation of the 
living stomata in situ, for any reasonable desired period, the 
method above outlined has a unique value for certain purposes. 
It will be found, I venture to believe, to be invaluable in supple- 
menting and checking the results obtained by such methods as 
that of alcoholic fixation (Lloyd, /. c.), of the hygroscope (of 
whatever type), of the porometer,t and of the stomatograph.t 
In using the method one must have a care for his eyes. The 
adjustment of the illumination must be done with the protection 
of a color screen, and for this purpose a leaf interposed in front 
of the objective has served well enough. Under field conditions, 
especially when one is working for a considerable length of time, 
dark eyeglasses are very desirable, more particularly if the sur- 
roundings are highly illuminated. Small circular discs of dark- 
tinted glass in various shades to be placed above the ocular have 
been found advantageous, more especially when the leaf is rather 
thin, say as thin as the leaf of the cotton. 
In the actual observation of the stomata the leaf is placed 
directly on the stage without any accessories in the form of glass 
slides or covers. It is held in position by gentle pressure upon it 
of the index and middle fingers, which, also, embrace the end of 
the objective. In the eyepiece a micrometer is placed. The 
absence of a glass slide, which is in any event unnecessary, brings 
the stomata nearer the focus of the condenser and so improves the 
definition. As one is dealing with a brilliant area of light, it is 
quite necessary to have it central, since oblique illumination 
causes bright reflections from the surface of the stomatal outer 
vestibule, which may mislead the observer. 
LEAF WATER IN PERCENTAGE OF DRY WEIGHT 
If we consult TABLE 1, which contains the percentages of 
leaf water calculated to dry weight for two parallel series, treated 
as nearly alike as possible, it will be seen that when so expressed 
EAS CEREIRRMIESS ATE a Rnke esas iser egal estes ee mio 
* An instrument of special design, now in course of construction, will obviate 
many inconveniences, 
+ Darwin, eres boas agate M. On a new method of estimating the 
aperture of stomata. Proc. Roy. Soc. B. 84: 136-154. 1911. 
t Balls, W. L. The “Stomatograph.” Nature 87:180. 10 Au ro1t. 
