60 



CIRCUMNUTATION OF SEEDLINGS. 



CHAP. I. 



After a time the apex is drawn out of the empty seed-coats, 

 and rises up, forming a right angle, or more commonly a still 

 larger angle with the lower part, and occasionally the whole 

 becomes nearly straight. The conical protuberance, which 

 originally formed the crown of the arch, is now seated on one 

 side, and appears like a joint or knee, which from acquiring 

 chlorophyll becomes green, and increases in size. In rarely or 

 never becoming perfectly straight, these cotyledons differ remark- 

 ably from the ultimate condition of the arched hypocotyls or 

 epicotyls of dicotyledons. It is, also, a singular circumstance 

 that the attenuated extremity of the upper bent portion 

 invariably withers and dies. 



A filament, 1'7 inch in length, was affixed nearly upright 

 beneath the knee to the basal and vertical portion of a 

 cotyledon; and its movements were 

 traced during 14 h. in the usual manner. 

 The tracing 'here given (Fig. 47) indi- 

 cates circumnutation. The movement of 

 the upper part above the knee of the same 

 cotyledon, which projected at about an 

 angle of 45 above the horizon, was 

 observed at the same time. A filament 

 was not affixed to it, but a mark was 

 placed beneath the apex, which was 

 almost white from beginning to wither, 

 and its movements were thus traced. The 

 Allium cepa : circumnu- figure described resembled pretty closely 

 tation of basal half that above given ; and this shows that the 



Fig. 47. 



of arched cotyledon, 

 traced in darkness on 

 horizontal glass, from 

 8.15 A.M. to 10 P.M. 

 Oct. 31st. Movement 

 of bead magnified 

 about 17 times. 



chief seat of movement is in the lower or 

 basal part of the cotyledon. 



Asparagus officinalis (Asparagese). 

 The tip of a straight plumule or cotyledon 

 (for we do not know which it should be 

 called) was found at a depth of '1 inch 



beneath the surface, and the earth was then removed all round 

 to the depth of -3 inch. A glass filament was affixed obliquely to 

 it, and the movement of the bead, magnified 17 times, was traced 

 in darkness. During the first 1 h. 15 m. the plumule moved to 

 the right, and during the next two hours it returned in a roughly 

 parallel but strongly zigzag course. From some unknown cause 

 it had grown up through the soil in an inclined direction, and 

 now through apogeotropism it moved during nearly '24 h. in 



