Ohai. l ipomcea. 47 



vertically to the hypoootyl of a seedling half an inch high ; and 

 its movements were traced during 50 h. on a horizontal glass 

 (Fig. 34). From some unknown, cause it bowed itself to one 

 side, anl as this was effected by a zigzag course, it probably 

 circumnutated ; but with hardly any other seedling observed 

 by us was this movement so obscurely shown. 



Ipomcea ccerulea vel Pharbitis nil (Convolvulacese). — Seedlings 

 of this plant were observed because it is a twiner, the upper 

 intemodes of which circumnutate conspicuously; but, like 

 other twining plants, the first few internodes which rise above 

 the ground are stiff enough to support themselves, and therefore 

 do not circumnutate in any plainly recognisable maimer.* In 

 this particular instance the iifth internode (including the hypo- 

 cotyl) was the first which plainly circumnutated and twined 

 round a stick. We therefore wished to learn whether oircum- 

 nutation could be observed in the hypoootyl if carefully observed 

 in our usual manner. Two seedlings were kept in the dark 

 with filaments fixed to the upper part of their hypocotyls ; but 

 from circumstances not worth explaining their movements were 

 traced for only a short time. One moved thrice forwards and 

 twice backwards in nearly opposite directions, in the course of 

 3 h. 15 m. ; and the other twice forwards and twice backwards 

 in 2 h. 22 m. The hypocotyl therefore circumnutated at a re- 

 markably rapid rate. It may here be added that a filament was 

 affixed transversely to the summit of the second intcrnude above 

 the cotyledons of a little plant 3| inches in height; and its 

 movements were traced on a horizontal glass. It circumnutated, 

 and the actual distance travelled from side to side was a quarter 

 of an inch, which was too small an amount to be perceived with- 

 out the aid of marks. 



The movements of the cotyledons are interesting from their 

 complexity and rapidity, and in some other respects. The 

 hypocotyl (2 inches high) of a vigorous seedling was secured to a 

 stick, and a filament with triangles of paper was affixed to one 

 of the cotyledons. The plant was kept all day in the hot-house, 

 and at 420 p.m. (June 20th) was placed under a skylight in 

 the house, and observed occasionally during the evening and 

 night. It fell in a slightly zigzag line to a moderate extent 

 from 4.20 p.m. till 10.15 p.m. When looked at shortly after mid- 

 night (12.30 P.M.) it had risen a very little, and considerably by 



• 'Movementa and Habite of Climbing Plants,' p. 33, 1S75. 



