102 Plant Growth- Rhythms. [Sess. 



light and darkness. Sachs concluded that an autonomic 

 variation underlay the daily periodicity, Baranetzsky that the 

 phenomenon was an induced one. 



My own investigations include an examination of root 

 periodicity which has hitherto not received as much atten- 

 tion as that of shoots, and regarding which there is a differ- 

 ence of opinion as to whether it exists or not. At the outset 

 it was necessary to devise a piece of apparatus for automati- 

 cally recording root-growth. 



This may be described as a U-tube, the curved part of 

 which is replaced by a metal box containing two light pulleys. 

 The tube is filled with water, and in one arm a seedling is 

 fixed with its root depending into the water, the root tip in 

 contact with a light float ; from the float a thread passing 

 over the two pulleys and up the other arm of the tube is 

 attached to the distal arm of a recording lever, the other arm 

 of which bears a pen making a trace on the clock-work drum 

 of the auxanometer. 



Long continuous records were taken extending from ten to 

 forty days. The experiments were carried on under the 

 natural conditions of illumination ; thus, instead of an artificial 

 twelve hours' day and twelve hours' night, which is only 

 occasionally found in nature, plants experimented on in 

 December were subjected to the natural daylight of eight 

 hours and darkness of sixteen hours, while in midsummer the 

 conditions were reversed. 



The tracing on the drum supplies data necessary for cal- 

 culating the amount of growth of the organ for any interval 

 of time, and for the construction of growth curves. For the 

 purpose of exact comparison of the growth of different organs 

 of the same plant, or of corresponding organs of different 

 plants, as the length of the growing region is not constant, it 

 is necessary to calculate the rate of growth — i.e., the amount 

 of growth per unit length taken as one millimetre per unit 

 time, one minute. The figure thus obtained is the Coefficient 

 of Growth. The Coefficient of Growth 



Amount of Growth 

 Length of Growing Eegion (in mms.) x Time (in minutes). 



Consideration of numerous experiments (' Proc. Eoy. Soc. 



