70 Sunons — Comparative Studies on the Rate of 



and leaves. Darwin worked on this species in a greenhouse 

 from May 13 till May 25, and obtained as his shortest time, 

 2 hours 5 minutes, with an average of 2 hours 50)^ minutes. 

 By taking advantage of every fresh sprout as it began to reach 

 for a support, the results appended were obtained. 



Growing in a protected corner of the garden was another 

 Wisteria, with long, strong stems, of which three were unsup- 

 ported. On August 18, these were gently secured to stakes, 

 two of them hanging just as on the vine, being secured at one 

 point to a stick to insure against wind interference, the third 

 being tied upright with about nine inches free. This began 

 its twisting in that position, but gradually became horizontal 

 from the point of attachment. Apparatus for marking was 

 set up and the following results obtained. All the stems were 

 exposed to direct sunlight except for a short time, when they 

 passed through an arc shaded by the plant itself 



The shortest time obtained was 2 hours, the average of all 

 observations 2 hours i 5 ^ minutes. 



As to the time of day when circumnutation is most rapid, 

 the following diagram was made from the foregoing records 

 of the five species examined. The temperature recorded for 

 a circumnutation represents the average for the hours between 

 which the circle was made. The temperature records are 

 suggestive, those during the shortest circumnutations ranging 

 from 25.5 C. to 36.5 C; of the longest, 15.5 C. to 30.5 C. 



From the table it will be noticed that of the 3 i quick twin- 

 ings, 22 are in the afternoon. Looking at the list of long 

 circumnutations 8 of 18 are in the afternoon. But a more 

 detailed analysis brings out some interesting results, that corre- 

 spond very closely with those given by Dr. Schively in the 

 paper already cited (pp. 296-97). The following statement is 

 there made regarding periodicity of circumnutation. " Begin- 

 ning with the early hours of morning, there is a gradual 

 acceleration until 11 or 11.30 a.m. The greatest rapidity 

 occurs from this time until 2 or even 3 p. m. After that time 



