1896] BRIEFER ARTICLES ce 
A horizontal microscope (with plate VI).— The laboratory for 
plant physiology can hardly be considered adequately equipped 
which does not possess a microscope adapted to measuring directly 
the vertical growth of plants. The auxanometer, in simple or com- 
plex form, is scarcely more indispensable. If no specially constructed 
instrument is available some makeshift must be devised to enable 
direct observation of growth. After utilizing common microscopes in 
various degrees of disorganization, but with unvarying dissatisfaction, 
the instrument illustrated by plate V7 was devised by the writer, in 
consultation with Dr. Rodney H. True, to facilitate whose researches 
it was immediately needed. 
It will be observed at a glance that the general idea of the instru- 
ment is that illustrated in Pfeffer’s Phystologie 2:85, fig. 8, which is 
essentially the form still used in the Leipzig laboratory. Upon com- 
parison, however, it will be readily seen that the instrument here des- 
cribed has a number of points of superiority in the accuracy, readi- 
ness, and range of adjustment. It was constructed from my drawings 
by the Bausch & Lomb Optical Co., of Rochester, N. Y., to whose 
courtesy I owe the illustration. 
The base is the large lead-filled brass tripod of their “ Investi- 
gator”’ stand, with leveling screws. This base is the only part which 
I now think could be improved. It would be better were it some- 
what larger and heavier. Its radial spread is now 10™; it might well 
be 12™ with correspondingly increased weight. From the base rises 
a tube 3 in external diameter, sawed at the top, where it is pinched 
by a screw collar. Within the outer tube slides a nickel draw-tube, 
22™ long, which can be set at any height, up to its maximum, by 
means of the screw collar. The upper end of the draw-tube carries a 
Pinion, with double milled heads, engaging a rack on a triangular 
slide. By means of this rack and pinion the body, which has been 
roughly brought to the required height by means of the draw-tube, 
can be accurately set. A finer adjustment has not been found neces- 
Sary, since a 1” objective has given the highest power required, and 
with this the micrometer lines can be made to coincide accurately 
with the tip of the object under observation. 
At right angles to the triangular slide is fixed a tube in which 
moves the nickeled body, actuated by a pinion which engages a rack 
on the body. This adjustment serves to focus the instrument. Above 
the pinion, between its milled heads, is fastened a spirit-level, accu- 
