CHAP. I. 



PEIMULA. 



45 



filament was, as far as could be ascertained, about "14 of an 

 inch. 



Hclianthus annuus (Composite). The upper part of the 

 hypocotyl moved during the 

 day-time in the course 

 shown in the annexed figure 

 (Fig. 32). As the line runs 

 in various directions, cross- 

 ing itself several times, 

 the movement may be con- 

 sidered as one of circumnu- 

 tation. The extreme actual 

 distance travelled was at 

 least *1 of an inch. The 

 movements of the cotyle- 

 dons of two seedlings were Helianthus annuus : circumnutation of 

 -, ,, . hypocotyl, with filament fixed across 



observed; onefacmg a north- it s summit, traced on a horizontal 

 east window, and the other glass in darkness, from 8.45 A.M. to 

 so feebly illuminated from 10 - 4 ' 5 P - M -' and for an hour on f llo w- 



ibnvP a<? tn bp ilmnsf in in mornin g- Movement of bead 

 above as to be almost in magnifie d 21 times, here reduced to 

 darkness. They continued one-half of original scale. 

 to sink till about noon, 



when they began to rise; but between 5 and 7 or 8 P.M. 

 they either sank a little, or moved laterally, and then again 

 began to rise. At 7 A.M. on the following morning those on 

 the plant before the north-east window had opened so little 

 that they stood at an angle of 73 above the horizon, and were 

 not observed any longer. Those on the seedling which had 

 been kept in almost complete darkness, sank during the whole 

 day, without rising about mid-day, but rose during the night. 

 On the third and fourth days they continued sinking without 

 any alternate ascending movement; and this, no doubt, was 

 due to the absence of light. 



Primula Sinensis (Primulacese). A seedling was placed with 

 the two cotyledons parallel to a north-east window on a day 

 when the light was nearly uniform, and a filament was affixed 

 to one of them. From observations subsequently made on 

 another seedling with the stem secured to a stick, the greater 

 part of the movement shown in the annexed figure (Fig. 33), 

 must have been that of the hypocotyl, though the cotyledons 

 certainly move up and down to a certain extent both during the 

 day and night. The movements of the same seedling were traced 



