CH. VIIl] TWINING PLANTS. 229 



the dot is to be made, and then to bring the pointer 

 sharply down on the glass. A little practice is needed 

 to get results with small amounts of movement. The 

 observations should at first be made at intervals of about 

 10 minutes, so that the observer may get an idea of 

 the rapidity with which the movement under observation 

 is proceeding. He may thus be able to regulate the 

 intervals between his subsequent observations so as not to 

 spend unnecessary time, and yet not to fail in getting a 

 fair idea of the movement. 



Fig. 43 l represents the circumnutation of a cabbage 

 seedling, from 9.15 a.m. to 8.30 a.m. on the following day, 

 the dots represent the actual marks made on the glass 

 with the sharpened wood, the lines and arrows being 

 added to show the course of the movement : the woodcut 

 is reduced to half the size of the original. No observations 

 were made at night : the broken line represents the change 

 of position which took place between the first evening 

 and the following morning. The tracing therefore (if the 

 broken line be neglected) practically represents the 

 circumnutation during a day of about 12 hours. 



(259) Circumnutation: twining plants 2 . 



The observations should be made either in a greenhouse 

 or indoors, on Humulus lupulus (the hop) and Phaseolus 

 multifloriis. The basal part of the plant should be tied to 

 a stick stuck in the soil of the pot, and 6 inches or a foot 



1 The tracing was made by a slightly different method to that here 

 described. 



a C. Darwin, Climbing Plants, Chapter i. 



