CHAP. VI. SLEEP OF COTYLEDONS. 309 



Trifolium. The germination of 21 species was observed. In 

 most of them the cotyledons rise hardly at all, or only slightly, 

 at night ; but those of T. glomeratum, striatum and incarnatum 

 rose from 45 to 55 above the horizon. With T. subterraneum, 

 leucanthemum and strictum, they stood up vertically ; and with 

 T. strictum the rising movement is accompanied, as we shall see, 

 by another movement, which makes us believe that the rising 

 is truly nyctitropic. We did not carefully examine the coty- 

 ledons of all the species for a pulvinus, but this organ was 

 distinctly present in those of T. subterraneum and strictum ; whilst 

 there was no trace of a pulvinus in some species, for instance, in 

 T. resupinatum, the cotyledons of which do not rise at night. 



Trifolium subterraneum. The blades of the cotyledons on the 

 first day after germination (Nov. 21st) were not fully expanded, 

 being inclined at about 35 above the horizon ; at night they 

 rose to about 75. Two days afterwards the blades at noon 

 were horizontal, with the petioles highly inclined upwards; 

 and it is remarkable that the nocturnal movement is almost 

 wholly confined to the blades, being effected by the pulvinus at 

 their bases ; whilst the petioles retain day and night nearly the 

 same inclination. On this night (Nov. 23rd), and for some few 

 succeeding nights, the blades rose from a horizontal into a 

 vertical position, and then became bowed inwards at about an 

 average angle of 10 ; so that they had passed through an angle 

 of 100, Their tips now almost touched one another, their 

 bases being .slightly divergent. The two blades thus formed 

 a highly inclined roof over the axis of the seedling. This 

 movement is the same as that of the terminal leaflet of the 

 tripartite leaves of many species of Trifolium. After an interval 

 of 8 days (Nov. 29th) the blades were horizontal during the 

 day, and vertical at night, and now they were no longer bowed 

 inwards. They continued to move in the same manner for the 

 following two months, by which time they had increased greatly 

 in size, their petioles being no less than '8 of an inch in length, 

 and two true leaves had by this time been developed. 



Trifolium strictum. On the first day after germination the 

 cotyledons, which are provided with a pulvinus, stood at noon 

 horizontally, and at night rose to only about 45 above the 

 horizon. Four days afterwards the seedlings were again ob- 

 served at night, and now the blades stood vertically and were 

 in contact, excepting the tips, which were much deflexed, so 

 that they faced the zenith. At this age the petioles are curved 



