Dec, 1903.] 



Notes on Nutation of Plants. 



31 



usually not more than 2o°-3o° east. During dr}- weather the 

 amount of nutation was increased by watering the plants. As in 

 the sunflower, the stem is usually straight by 10 o'clock at night. 

 Ambrosia artemisaefolia was studied and found to nutate well, 

 as reported by Stevens. Ambrosia psylostachya and Xanthium 

 speciosum also nutate, considerable movement of the stem being 

 readily observed during favorable conditions. Helianthus maxi- 

 miliani, H. grosseserratus, H. hirsutus, and H. tubersus nutate 

 well before anthesis. H. maximiliani is especially striking on 



Fig. I. 



Fig. 



Fig. I. Helianthus annuus nutating to the west at 7 p. M. 

 Fig. 2. Ambrosia trifida at 7 p. m. Both from Clay Co., Kansas. 



occount of its stout stem and slender, rigid leaves. On favorable 

 days the nutation is 90° west in the evening and 20° or more east 

 in the morning. 



Although Stevens gives Amaranthus as a genus which shows 

 nutation, he does not name the species observed. During the 

 past summer two species were studied by the writer, namely, 

 Amaranthus hybridus and A. retroflexus. The first nutates the 

 more prominently both in the morning and evening, probably be- 

 cause of its more slender stem. The process is much the same as 

 in the sunflowers, but the curve in the stem is not nearly so 

 abrupt. However, on favorable evenings the terminal rosette 

 faces the setting sun to such an extent that the rays of light fall 

 on the broad surface of the leaves at right angles. 



