1891. The Growth-Periodicity of the Potato-Taber. 465 
battery, but interpolated in the circuit was the electric clock, so 
adjusted that every hour the circuit was closed for a few seconds. 
During the closure of the circuit the electro-magnet attracted 
the armature, overcoming the tension of the spring and releasing 
one cog of the ratchet-wheel. By this means the vertical cylinder 
turned about one-sixteenth of an inch with the hands of the 
watch, and the tracing needle made a horizontal mark upon the 
smoked paper covering the cylinder. The opening of the circuit 
as the hands passed by the hour released the armature, allowed 
the spring to pull back the lever, and stopped the clock-work until 
the next hour, when a similar horizontal mark was made. During 
the hours, then, any expansion of the tuber would loosen the string 
attached to the jacket. Pulling against this the weights would 
turn the first wheel. This would turn the second wheel, and the 
indication of growth, one hundred times magnified, but in proper 
ratio, would appear as vertical tracings upon the smoked cylinder. 
This brief description of the Baranetski apparatus is given that 
the exact method of research may be apparent. 
The first experiments upon the growing tuber, made in accord- 
ance with the method described in the Botanical Gazette, were 
Satisfactory in so far that they demonstrated the availability of 
e Baranetski apparatus for the purpose for which it was 
employed. In one of the early experiments a trace of periodic 
growth was distinguished, but it did not seem to be sufficient to 
justify any confident assertion of periodicity. The first experi- 
Ment continued two weeks. During this time the needle kept 
falling ; at the close of the experiment it was about half an inch 
below its original level. In the second experiment certain drops 
in the tracings, usually in the early morning, were noticed, but I 
have since come to believe that not all of these were true growth- 
tracings, but were due, at least in part, to changes of temperature 
of the soil, the strings, and the atmosphere, with consequent 
enings, relaxations, and alterations in the needle-position. 
Against such accidental and confusing records there was a con- 
stant necessity of guarding. In general, a conservative statement 
of conclusions from these experiments with the single wheel is 
as follows : 
