358 Growth-Periodicity of the Potato Tuber. 



second wheel was passed the thread bearing the tracing needle at 

 one end and a small counterpoise at the other. The tracing needle 

 was brought up against the smoked cylinder of the registering ap- 

 paratus. This rested upon a clock-work in which a rachet-wheel 

 was caught by a lever attached by a spring and bearing at the 

 opposite end an armature near the pvoles of a small electro-mag- 

 net. Connected with the electro-magnet was a battery, but inter- 

 polated 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, overcom- 

 ing the tension of the spring and releasing one cog of the ratchet 

 wheel. By this means the cylinder attached to the clock-work 

 turned about 1-16 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 the hour released the armature, allowed the spring 

 to push back the lever and stopped the cylinder clock-work until 

 the next hour when a similar horizontal mark was made. During 

 the hours, then, any expansion in the potato-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 100 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 ac- 

 cordance with the method described in the Botanical Gazette, were 

 satisfactory in so far that they demonstrated the availability of the 

 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 base any con- 

 fident assertion of periodicity upon. The first experiment con- 

 tinued two weeks. During this time the needle kept falling and 

 at the close of the experiment was about half an inch below the 

 level of the beginning. In the second experiment certain drops 

 in the tracings, usually in the early morning, were noticed, but I 

 have come to believe that these were not true growth-tracings but 

 due to changes in temperature of the soil, the strings and the at- 

 mosphere with consequent shortenings and expansions. Against 

 such accidental and confusing records as these it was constantly 



