464 The American Naturalist. [ May, 
in our later experiments the wheel attached to the tuber-thread 
does not bear the tracing needle, but carries another thread on its 
large circumference, which runs to the small circumference of the 
tracing wheel. By this means hourly registrations are obtained 
instead of three-hour registrations as by the first method. 
To recapitulate the method as finally developed: A potato- 
plant, grown in a box from which one end had been removed, 
was selected and carried to the experimenting room. With due 
care a tuber was exposed, and under it, resting upon the bottom 
of the box, a wooden block was placed in such a way that down- 
ward pressure would not disturb the position of the tuber. The 
root-stock umbilicus was protected from desiccation or injury 
during these processes of blocking up. Next a wooden jacket 
consisting of two squares of cigar-box material, held together by 
a number of slightly stretched rubber-bands, was fitted over the 
tuber in such a way that one square of the cigar-box wood 
clung to the block below and the other piece was parallel, but on 
the upper side of the tuber. To the center of this upper square 
a small screw was fixed, and to this screw afine silver wire was 
tied—since thread was rotted by the soil,—and this wire, after 
the whole apparatus of block, tuber, and jacket was covered with 
earth again, came to the surface of the soil under the first wheel 
of the auxanometer. An inch and a half above the ground a 
twisted linen thread, which gave better friction on the wheel, was 
attached to the silver wire, and this twisted thread was 
over the small circumference of the first wheel and drawn taut 
by a weight of about forty grams. Passing from the large 
circumference of the first wheel to the small circumference of the 
second was a linen thread equally weighted at each end,and over 
the large circumference of the second wheel was passed a th nail 
bearing at one end the tracing needle and at the other & a 
counterpoise. The tracing needle was placed in come K 
the vertical smoked cylinder of the registering apparatus. | 
rested upon a clock-work in which a ratchet-wheel was "> — 
by a lever attached to the clock-work by a spring and Deal” 
at the opposite end an armature near the poles of a small clee 
magnet. Connected with the magnet was a two-celled Laf 
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