Groivth-Pcriodicity of the Potato Tuber. 359 



necessary to guard. In general the conclusions from experiments 

 with the single wheel were conservatively stated as follows : 



(a) The apparatus as set up indicates growth, by cylinder 

 tracings. 



(h) A possible trace of periodicity in the growth might have 

 manifested itself. 



Further than this we did not feel at liberty to go, under the 

 conditions of the experiment. 



Desiring to obtain more perfect results and to solve the ques- 

 tion of the manner of growth of the tuber, the improved method 

 of setting of the apparatus described above was developed, and the 

 first experiment gave very favorable and luminous results. 



The experiment began with a tuber about ^ inch in diameter. 

 At this time the top of the plant had begun to die from the at- 

 tack of a blight. After attachment the registering needle gave 

 two or three sharp drops owing to the stretching of strings and 

 general getting-into-equilibrium of the apparatus. After this 

 stage was passed the needle began dropping very gradually. This 

 gradual descent was continued from 8 o'clock in the evening until 

 about 8 o'clock in the morning. At this time the drop ceased and 

 horizontal tracings continued until about 1 130 p. m., when a short 

 abrupt drop was registered, followed by a longer drop, then by 

 one shorter than the second but longer than the first, next by one 

 longer than any, closely succeeded by another long one. After 

 this the registrations were short and the regular gradual fall until 

 8 a. m. began. Here again the horizontal mark began and con- 

 tinued until 2 p. m., when a second drop began, on a somewhat 

 smaller scale than the one registered the first day. The total ex- 

 tent of the second day's maximum between 2 p. m. and 8 p. m., 

 was about one-half that of the first day's maximum. The third 

 day the same tracings continued — only the tracings of the maxi- 

 mum were very much reduced — not more than one-quarter, in 

 total length, of the second day's tracings. The fourth day's trac- 

 ings were like those of the second day in all particulars, and those 

 of the fifth day likewise, except that the tracings showed a less 

 maximum growth. The sixth day was peculiar. During this 

 day no appreciable drop in the tracings was detected. The ex- 

 planation of this cessation is not offered. It may be said, how- 

 ever, that the death of the top was now about complete so far as 

 the leaves and secondary branches were concerned. Only in the 



