CHAP. IV. CIRCUMNUTATION OF STEMS. 203 



found to be in constant movement. It crossed five divisions of 

 the micrometer, that is, -^th of an inch, in 6 m. 20 s. There 

 could hardly be a doubt that it was the stem which chiefly 

 moved, for the tip did not get quickly out of focus ; and this 

 would have occurred had the movement been confined to the 

 leaf, which moves up or down in nearly the same vertical plane. 



(3.) Linum usitatissimum (Linese, Fam. 39). The stems of this 

 plant, shortly before the flowering period, are stated by Fritz 

 Mliller (' Jenaische Zeitschrift,' B. v. p. 137) to revolve, or 

 circumnutate. 



(4.) 'Pelargonium zonale (Geraniacese, Fam. 47). A young 

 plant, 7s inches in height, was observed in the usual manner ; 

 but, in order to see the bead at the end of the glass filament 



Fig. 71. 



Pelargonium zonale: circumnutation of stem of young plant, feebly illu- 

 minated from above. Movement of bead magnified about 11 times ; 

 traced on a horizontal glass from noon on March 9th to 8 A.M. on 

 the llth. 



and at the same time the mark beneath, it was necessary to cut 

 off three leaves on one side. We do not know whether it was 

 owing to this cause, or to the plant having previously become 

 bent to one side through heliotropism, but from .the morning of 

 the 7th of March to 10.30 P.M. on the 8th, the stem moved 

 a considerable distance in a zigzag line in the same general 

 direction. During the night of the 8th it moved to some 

 distance at right angles to its former course, and next morning 

 (9th) stood for a time almost still. At noon on the 9th a new 

 tracing was begun (see Fig. 71), which was continued till 8 A.M. 

 on the llth. Between noon on the 9th and 5 P.M. on the 10th 

 (i.e. in the course of 29 h.), the stem described a circle. This 

 plant therefore circumnutates, but at a very slow rate, and to a 

 small extent. 



(5.) Tropceolum mafus (?) (dwarfed var. called Tom Thumb) ; 

 (Geraniaceso, Fam. 47). The species of this genus climb by the 



