1902] MICROSCOPICAL JOURNAL. 69 
of the centre away from the stop, and in addition slightly 
altering the illumination to get the best definition in 
both views. By these means the stereoscopic effect may 
be very much improved, and some remarkable results ob- 
tained in relation to the structure of insect scales and 
diatoms, which is still a question of uncertainty.—F. H. 
WENHAM, in Hnglish Mechanic. 
PREPARING TISSUES FOR PHOTOMICROGRAPHY.—A good 
deal of care is required in staining tissues so as to diff- 
erentiate between the various systems that occur in such 
a structure as a stem or root andin the choice of stains, 
so as to render the light coming through these parts suf- 
ficiently actinic for the photographic plate. Such stains 
as eosin are, of course, eminently suited for the demon- 
stration of such structures as the sieve-plates of sieve- 
tubes, but it is doubtful if the red light that comes through 
is very powerful actinically ; and in cases such as these it 
would perhaps be more satisfactory to rely upon drawings 
taken from actual observation than upon the photomicro- 
graph. In the photography of most transverse sections 
of stems, roots, and many other botanical specimens we 
may use with advantage as our staining material either 
toluidin-blue, haematoxylin, or both, for tissues with them 
turn a beautifully actinic blue on treatment with tap- 
water (not distilled water, because it requires the minute 
degree of alkalinity that tap-water possesses). We have 
obtained very satisfactory results with this method. In 
regard to differential staining a combination of methyl- 
green and toluidin-blue, or separate staining with these 
two, would give good results, as the actinic power of the 
former is much less than that of the latter. Tissues stained 
with eosin or carmine will, of course, give a result; but — 
it is difficult to obtain good definition, and the cell-walls, 
etc., only come out faintly, with somewhat blurred out- 
_ lines, But a differential stain with eosin and toluidin- 
