•JHAP. r. CEEINTHE. 48 



downwards in the evening. Therefore their weight, which is 

 considerable when almost fully developed, probably came into 

 play in originally determining the downward movement. The 

 periodicity of this movement is much influenced by the degree 

 of light to which the seedlings have been exposed during the 

 day; for three kept in an obscure place began to siLk about 

 noon, instead of late in the evening ; and those of another seed- 

 ling were almost paralysed by having been similarly kept during 

 two whole days. The cotyledons of several other species Lf 

 Ipomoea likewise sink downwards late in the evening. 



Cerinthe major (Boragineae). — The circumnutation of the 

 hypocotyl of a young seedling with the cotyledons hardly 



Fig. 36. 



Cerinthe major; circumnutation of hypocotyl, with lilament fixed across ita 

 summit, illuminated from above, traced on horizontal glass,- from 

 9.26 A.M. to 9.53 P.M. on Oct. 25th. Movement of the bead magnified 

 30 times, here reduced to one- third of original scale. 



expanded, is shown in the annexed figure (Fig. 36), which 

 apparently represents four or five irregular ellipses, described 

 in the course of a little over 12 hours. Two older seedlings 

 were similarly observed, excepting that one of theifl was kept 

 in the dark ; their hypocotyls also circumnutated, but in a more 

 simple manner. The cotyledons on a seedling exposed to the 

 light fell from the early morning until a little after noon, and 

 then continued to rise until" 10.30 p.m. or later. The cotyledons 

 of this same seedling acted in the same general manner during 

 the two following days. It had previously been tried in the 

 dark, and after being thus kept for only 1 h. 40 m. the cotyledons 

 began at 4.30 p.m. to sink, instead of continuing to rise till late 

 at night. 



