Grozvth-Periodicity of the Potato Tuber. 357 



up apparatus, and by two or three helpful suggestions concern- 

 ing certain technical difficulties which presented themselves in 

 the course of our investigations. The method of research first 

 adopted by us is described somewhat in detail in the Botanical 

 Gazette, May, i8qi ; but upon this method certain improvements 

 have been made. The apparatus used was the Baranetski self- 

 registering auxanometer with electric-clock attachment, man- 

 ufactured by Albrecht of Tubingen. At first both wheels of the 

 apparatus were not employed but afterwards it was found that 

 the two wheels could be combined in such a way as to multiply 

 the tracings tenfold, and in our later experiments the wheel at- 

 tached 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 were obtained instead of three-hour regis- 

 trations as by the first method. 



To recapitulate the method finally adopted as developed : A 

 potato plant grown in a box from which one end had been re- 

 moved was selected and carried to the experimenting room. With 

 due care a tuber was exposed, and under it, resting upon the bot- 

 tom of the box, a wooden block was placed in such a way that 

 downward pressure would not disturb the position of the tuber. 

 The rootstock 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 lay 

 upon the block below and the other was parallel with it, but on 

 the opposite side of the tuber. To the center of this upper square 

 a screw was fixed and to this screw a silver wire was tied — since 

 thread was rotted by the soil — and this wire after the whole ap- 

 paratus of block and jacket was covered with soil, came to the 

 surface of the soil under the first wheel of the auxanometer. An 

 inch or two above the ground a twisted linen thread which gG.ve 

 better friction on the wheel was attached to the silver wire, and 

 this twisted thread was passed 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 



