310 



MODIFIED CIECUMNUTATION. 



Chap. VI. 



upwards, and at night, when the bases of the blades are in con- 

 tact, the two petioles together form a vertical ring surrounding 

 the plumule. The cotyledons continued to act in nearly the same 

 manner for 8 or 10 days from the period of germination; but 

 the petioles had by this time become straight and had increased 

 much in length. After from 12 to 14 days the first simple true 

 leaf was formed, and during the ensuing fortnight a remarkable 

 movement was repeatedly observed. At I. (Fig- 125) we have 

 a sketch, made in the middle of the day, of a seedling about 

 a fortnight old. The two cotyledons, of which Sc is the 

 light, and Lc the left one, stand directly opposite one another. 



TrifoUwn strictum : diurnal and nocturnal positions of the two cotyledons 

 and of the first leaf. I. Seedling viewed obliquely from above, durin? 

 the day : Ho, right cotyledon ; Lc, left cotyledon ; F, first true leaf. 

 II. A rather younger seedling, viewed at night: lie, right cotyledon 

 raised, but its position not otherwise changed ; Lc, left cotyledon raised 

 and laterally twisted; F, first leaf raised and twisted so as to face the 

 left twisted cotyledon. III. Same seedling viewed at night from the 

 opposite side. The back of the first leaf, F, is here shown instead of 

 the front, as in II. 



and the first true leaf (F) projects at right angles to them. At 

 night (see II. and III.) the right cotyledon (Be) is greatly 

 raised, but is not otherwise changed in position. The left 

 cotyledon (Lc) is likewise raised, but it is also twisted, so that 

 its blade, instead of exactly facing the opposite one, now stands 

 at nearly right angles to it This nocturnal twisting movement 

 is affected not by means of the pulvinus, but by the twisting of 

 the whole length of the petiole, as could be seen by' the curved 

 line of its upper concave surface. At the same time the true 

 leaf (F) rises up, so as to stand vertically, or it even passes the 

 vertical and is inclined a little inwards. It also twists a little, 

 by which means the upper surface of its blade fronts, and 

 almost comes into contact with, the upper surface of the twisted 



