CHAP. IV. CIRCUMNUTATION OP LEAVES. 201 



the next day. The course followed was curvilinear or 

 straight, or slightly or strongly zigzag, and little loops 

 or triangles were often formed. A single large irregular 

 ellipse may be described on one day, and two smaller 

 ones by the same plant on the next day. With Drosera 

 two, and with Lupinus, Eucalyptus and Pancratium, 

 several were formed each day. 



The oscillatory and jerking movements of the leaves 

 of Dionsea, which resemble those of the hypocotyl of 

 the cabbage, are highly remarkable, as seen under the 

 microscope. They continue night and day for some 

 months, and are displayed by young unexpanded leaves, 

 and by old ones which have lost their sensibility to a 

 touch, but which, after absorbing animal matter, close 

 their lobes. We shall hereafter meet with the same 

 kind of movement in the joints of certain Graminese, 

 and it is probably common to many plants while cir- 

 cumnutating. It is, therefore, a strange fact that no 

 such movement could be detected in the tentacles of 

 Drosera rotundifolia, though a member of the same 

 family with Dionsea ; yet the tentacle which was ob- 

 served was so sensitive, that it began to curl inwards 

 in 23 seconds after being touched by a bit of raw meat. 



One of the most interesting facts with respect to 

 the circumnutation of leaves is the periodicity of their 

 movements ; for they often, or even generally, rise a 

 little in the evening and early part of the night, and 

 sink again on the following morning. Exactly the 

 same phenomenon was observed in the case of coty- 

 ledons. The leaves in 16 genera out of the 33 which 

 were observed behaved in this manner, as did probably 

 2 others. Nor must it be supposed that in the remain- 

 ing 15 genera there was no periodicity in their move- 

 ments ; for 6 of them were observed during too short 

 a period for any judgment to be formed on this head, 



