120 THE MICROSCOPE. Aug 
those of V. sessilis, the oogonia measuring 50 by 70 mm. 
Now as the mature spores (or oospores) are usually about 
the same size as the oogonia and threads, the inference 
seems to be that plants of this genus may fructify at any 
stage of growth. Otherwise, how is the discrepancy 
between the presumably last year’s spores and the new 
oogonia to be accounted for? ‘Then, further, as Cooke 
gives 70 mm., and not 100 mm., for the size of the spores 
of V. sessilis, what species is this likely to be? —W. P. 
Hamilton, Shrewsbury. 
Sharpening Microtome Knives.—I have used the No. 
2 Carborundum of the ‘sizes’ 220, 1 minutes and 10 minutes, 
suppled by the Carborundum Company, Monongahela City, 
Pa. ‘That it is possible after the knife has once been 
ground to shape to grind out a bad nick ina few minutes, 
which greatly minimizes the annoyance of cutting resis- 
tant tissues. After the edge has been smoothed as muchas 
possible with the finest grade of carborundum, diamantine 
is used. Moll recommends using one side of the plate for 
grinding and the other for polishing the edge. ‘To grind 
into shape the edge of the knife or razor as furnished by 
the manufacturer is a matter of considerable difficulty, and 
‘here in particular carborundum or is almost indispensable. 
Those possessing microtomes in which razors can be 
clamped will probably find it more convenient to obtain 
thick razorsalready ground to shape and with the super- 
fluous part of the cutting edge removed, as advocated by 
Moll. Such razors, of good English manufacture, slightly 
hollow-ground, and having a cutting edge measuring about 
14-16 degrees, are sold by P. J. Kipp & Zonen, Delft, 
Holland, for $2.50. A glass plate mounted on a wooden 
block for for sharpening the same can be had for $1.25. 
These razors are rigid, in this respect very different from 
the thin, very hollow-ground ones usually found on the 
market. They have an anvantage over knixes in being 
more easily handled, besides being ceeaper and easier to 
protect from injury when not in use.—W, T. Swingle in 
Science. 
