260 CIRCUMNUTATION OF LEAVES. Chap- I^ 



amongst ordinary and gynmospermous Dicotyledons 

 and amongst Monocotyledons, together with several 

 Cryptogams, have now been described. It would, 

 therefore, not be rash to assume that the growing 

 leaves of all plants circumnutate, as we Jiave seen 

 reason to conclude is the case with cotyledons. The 

 seat of movement generally lies in the petiole, but 

 sometimes both in the petiole and blade, or in the 

 blade alone. The extent of the movement differed much 

 in different plants ; but the distance passed over was 

 never great, except with Pistia, which ought perhaps 

 to have been included amongst sleeping plants. The 

 angular movement of the leaves was only occasionallv 

 measured ; it commonly varied from only 2° (and pro- 

 bably even less in some instances) to about 10'; but 

 it amounted to 23' in the common bean. The move- 

 ment is chiefly in a vertical plane, but as the ascending 

 and descending lines never coincided, there was always 

 some lateral movement, and thus irregular ellipses 

 were formed. The movement, therefore, deserves tc 

 be called one of circumnutation ; for all circumnuta- 

 ting organs tend to describe ellipses, — that is, growth 

 on one side is succeeded by growth on nearly but not 

 quite the opposite side. The ellipses, or the zigzag 

 lines representing dra\iTi-out ellipses, are generally 

 very narrow ; yet with the Camellia, their minor axes 

 wore half as long, and with the Eucalyptus more than 

 half as long as their major axes. In the case of Cissus 

 parts of the figure more nearly represented circles than 

 ellipses. The amount of lateral movement is therefore 

 sometimes considerable. Moreover, the longer axes 

 of the successively formed ellipses (as with the Bean 

 Cissus, and Sea-kale), and in several instances the' 

 zigzag lines representing ellipses, were extended in 

 very different directions during the same day or on 



