306 MODIFIED CIKCUMNUTATION. Chap. \L 



beneath the horizon. The nocturnal pcsition depends chiefl5 

 on the curvature of the petiole close to the blade, but the whole 

 petiole Ijecomes shghtly curved downwards. It deserves notice 

 that seedhngs of this and the last-named species were raised at 

 the end of February and another lot in the middle of March, 

 and the cotyledons in neither case exhibited any nyctitropic 

 movement. 



Ipomaa hona-nox. — The cotyledons after a few days grow to 

 an enormous size, those on a young seedling being 3j inches 

 in breadth. They were extended horizontally at noon, and at 

 10 P.M. stood at 63° beneath the horizon. Five days after- 

 wards they were 4i inches in breadth, and at night one stood at 

 64° and the other 48° beneath the hori,zon. Though the blades 

 are thin, yet from their great size and from the petioles being 

 long, we imagined that their depression at night might be 

 determined by their weight ; but when the pot was laid hori- 

 zontally, they became curved towards the hypocotyl, which 

 movement -could not have been in the least aided by their 

 weight, at the same time they were somewhat twisted upwards 

 through apogeotropism. Kevertheless, the weight of the coty- 

 ledons is so far influential, that when on another night the pot 

 was turned upside down, they were unable to rise and thus to 

 assume their proper nocturnal position. 



Ipom-j-a cbccinm. — The cotyledons whilst young do not sink 

 at night, but when grown a little older, but still only "4 inch in 

 length (measured as before) and -82 in breadth, they became 

 greatly depressed. In one case they were horizontal at noon, 

 and at 10 p.m. one of them stood at 64° and the other at 47° 

 beneath the horizon. The blades are thin, and the petioles, 

 which become much curved down at night, are short, so that 

 here weight can hardly have produced any effect. With all the 

 above speries of Ipomoea, when the two cotyledons on the same 

 seedling were imequally depressed at night, this seemed to 

 depend on the position which they had held during the day 

 with reference to the light. 



Solaiium lycopersicum (Solaneffi). — The cotjdedons rise so 

 much at night as to come nearly in contact. Those of S. palina- 

 caiithum were horizontal at noon, and by 10 p.m. had risen only 

 '27° 30' ; but on the following morning before it was light they 

 stood at 59° above the horizon, and in the afternoon of the same 

 d ly were again horizontal. The behaviour of the cotyledons oi 

 tliis latter species seems, therefore, to be anomalous. 



