y 
$ , MICROSCOPY. 249 
to the pint) and keep it at a temperature of 75° F. for nearly two 
weeks. The fungus of fermentation will reduce the potato to a 
pulp, except the vascular bundles which may be mounted in gum 
or balsam and studied with a power of one hundred diameters. 
They constitute a beautiful object, the pointed forms leading ` 
toward the eyes being distinctly seen. 
He notices that different varieties of potatoes are affected in a 
widely different manner by the potato-rot fungus (Peronospora 
in festans) , the Jackson White, for instance, being unaffected when 
the Early Rose growing in the same field were wholly destroyed by 
fungi. He believes it probable that, other things being equal, 
those varieties of potatoes’ which have the smallest air passages 
will be least affected by the fungus. The Santa Fé potatoes re- 
sisted fungoid and infusorial action far better than any other vari- 
eties tested, and it is claimed that they also, when growing in the 
field, resist the “rot” which destroys the varieties STONY cul- 
tivated in this country. d 
Microscopic Drawrxe. — Wishing to make a neutral tint re- 
flector, and while planning a frame in which to mount it, it occurred 
to me that a reflector to take the place of the steel disk of Soem- 
mering might be made by mounting a piece of looking-glass in the 
same .way as.a'neutral tint reflector, but with the silvering re- 
moved except a small disk less than the size of the pupil. On 
trial I found the reflection good, but the thickness of the glass 
looked through in such an oblique position tinted the field. In 
order to avoid this I made a mirror with a small disk of tin-foil 
wet with mercury and placed on the centre of a thin glass cover. 
This I mounted as before, and found it to work perfectly. This 
little contrivance which can be made by any one of ordinary me- 
chanical ability will take sig place perfectly of — expensive 
camera lucida. 
I made another, using wood in place of on, I centred a 
‘Piece of wood and turned a place for the cap end of the ocular 
and a smaller hole the rest of the distance through the bit of 
wood; turned the outside in the form of a cylinder and sawed 
off the end in a mitre-box to an angle of forty-five degrees ; then’ 
bored a one-half inch hole near the end of the tube for the re- 
flected rays, and turned a disk with a cell for the mirror and fitted 
: : e thin glass, cea it in with a small ring g of wood glued over | 
