678 Wisconsin Academy of Sciences, Arts, and Letters. 
based on the appearance of the strata as so seen. In this case 
tbey are of course approximately at right angles to tbe plane of 
tbe slide and appear sharply defined. 
Tbe starch grains in tbe rhizome of Ganna have been 
found to be specially favorable for comparative studies of tbe 
unstained and the stained grains. The attempt has been suc¬ 
cessfully made to identify a layer or series of layers in an un¬ 
stained grain and then in the same grain to determine success¬ 
ively the effect of different stains on these same layers. The 
material was fixed in Flemming’s weaker solution and) imbed¬ 
ded in paraffin. Microtome sections 10 ^ in thickness were 
used. The sections were fixed to the slide and the paraffin re¬ 
moved by xylol, the xylol removed by absolute alcohol, and the 
sections were then mounted and examined in water. 
I selected a large grain from a slide prepared in this 
manner. At the posterior end of the grain there appeared 
two broad, highly refractive layers (PL XL, Fig. 42 A, a and 
b). These are broadest in the middle line of the grain and 
thin out gradually to the sides. Between these layers there is 
a layer (1) which has the appearance of being an open water 
space It is thickest at the median line and tapers gradually 
to the sides. Toward the hilum from b there is a dark, 
slightly refractive layer separated from b by a dark line. This 
layer appears to be divided, the inner poition being paler in 
color. The remaining layers of the grain appear but faintly^ 
with the exception of those immediately surrounding the hi¬ 
lum, which are fairly distinct. The appearance of this grain 
as just described is that seen in median optical section. If 
the focus is raised or lowered we may get the appearance of 
light layers where there were dark layers and vice versa. This 
is due of course to the curvature of the layers, a change in 
focus bringing into view the next inner or outer layer which 
may be different in refractive index. 
The grain above described, mounted in water, is magnified 
980 diameters and drawn by the aid of a camera lucida. If 
now the grain is kept under observation and a dilute aqueous 
solution of iodine drawn under the cover by placing drops of 
the solution at one side and filter paper at the other, the grain 
