CHAP. IV. DICOTYLEDONS. 249 



(22.) Petunia violaaa (Solanese, Fam. 157). A very young 

 leaf, only -| inch in length, highly inclined upwards, was observed 

 for four days. During the whole of this time it bent outwards 

 and downwards, so as to become more and more nearly hori- 

 zontal. The strongly marked zigzag line in the figure on p. 248 

 (Fig. Ill), shows that this was effected by modified circum- 

 nutation ; and during the latter part of the time there was much 

 ordinary circumnutation on a small scale. The movement in 

 the diagram is magnified between 10 and 11 times. It exhibits 

 a clear trace of periodicity, as the leaf rose a little each evening ; 

 but this upward tendency appeared to be almost conquered by 

 the leaf striving to become more and F - 112 



more horizontal as it grew older. The 

 angles which two older leaves formed 

 together, were measured in the even- 

 ing and about noon on 3 successive 

 days, and each night the angle de- 

 creased a little, though irregularly. 



(23.) Acanthus mollis (Acanthacese, 

 Fam. 168). The younger of two 

 leaves, 2} inches in length, petiole 

 included, produced by a seedling 

 plant, was observed during 47 h. 

 Early on each of the three morn- 

 ings, the apex of the leaf fell ; and 

 it continued to fall till 3 P.M., on 

 the two afternoons when observed. 

 After 3 P.M. it rose considerably, and 

 continued to rise on the second night 

 until the early morning. But on 

 the first night it fell instead of rising, 

 and we have little doubt that this Acanthus mo//ts:circumnuta- 

 was owing to the leaf being very tion of young leaf, traced 

 young and becoming through epi- % l^^ 

 nastic growth more and more hori- of leaf n inches f rom the 

 zontal ; for it may be seen in the vertical glass, so movement 

 diagram (Fig. 112), that the leaf stood considerably magnified. 

 , . , ,, ,. , ,, Figure here reduced to one- 



on a higher level on the first than on ha f f of ori?inal scale . 



the second day. The leaves of an Temp. 15-16 C. 

 allied species (A. spinosus) certainly 



rose every night ; and the rise between noon and 10.15 P.M., 

 when measured on one occasion, was 10. This rise was chiefly 



