310 Schively — Contributions to the Life History of 



where the temperature often was 90 F. While there was 

 no sunlight, para-heliotropic positions were not assumed. 

 Certain it is that sunlight has a direct influence ; it has 

 been found that leaflets toward the east, for instance, may- 

 be visibly affected by the rays falling upon that side of the 

 plant, while those toward the west still remain normal. 



A plant whose leaves have taken the para-heliotropic 

 position, if shaded, or lifted to a shady spot, will show the 

 ordinary position in from three to seven minutes. 



The simple leaves rise slowly ; in a very young plant 

 they rise 90 and bend over toward the tender shoot. (Plate 

 XXV, Fig. 2.) In older plants they rarely rise more 

 than 75 . 



In all of the above movements, the angle of the petiole 

 seems unchanged ; leaflets and their pulvini alone being 

 concerned. 



A very hot sun causes the under surface to turn com- 

 pletely uppermost, the leaflets appear limp and droop. In 

 some species of plants, where this condition is seen, the 

 blades are firm at least when they are handled ; but in 

 Amphicarpaa, I think the expression used, best describes 

 their peculiar appearance. 



This movement is not apparent in all the leaves, usually 

 only the three or four nearest the upper part of the plant. 

 This behavior was noticeable upon hot days in the green- 

 house as well as out of doors. Macfarlane 21 first drew 

 attention to the above condition, as occurring in numerous 

 other plants, some of which are not at all sensitive accord- 

 ing to the ordinary application of this word. After the 

 intensity of illumination subsides, the leaflets gradually 

 assume the para-heliotropic position, or may even return to 

 the normal without the above transition. 



c. Nyctitropic position. In preparing to assume the nyc- 

 titropic position, the terminal leaflet falls slowly, the lateral 

 do likewise, gradually turning their upper surfaces toward 

 the terminal leaflet at an angle of 45 °. The complete de- 

 flexing may not take place until an hour after preparations 



