1899.] NATURAL SCIENCES OF PHILADELPHIA. Ill 



joined with the weaker maiu stems iu this northwestern curve. Even 

 where the main stems by some accident had a southern or eastern 

 leaning, the branchlets had the northwestern curve. Observations 

 were continued till the evening of September 4, all resulting iu the 

 fact that the general rule in this species was that the curving was 

 at nightfall northeastwardly; at 6.30 A.M., erect; at noon, with a 

 slight curve, and at 6 P.M., a strong curve northeastwardly. 



On September 6, Helianthus Mazimilianis had develoned con- 

 siderably toward a flowering state. At 7 P.]\I., all the flower 

 stems were bending shghtly westwardly. On the 7th, at 7 A.M., 

 all trending eastwardly; at 6 P.M., westwardly. On the 8th, 

 9th and 10th, the observations were the same. There was no 

 opportunity to note the direction of the stems at midday, but on 

 'the 11th they were nearly erect, but Avith a very shght eastern 

 trend. At 5 P.M., quite erect. By this time the ray florets of 

 the terminal head of flowers w^ere expanding, and no curving was 

 noted subsequently. 



In these observations I thought to note whether the curving was 

 due to an uncoiling of the spiral growth, or was done by a direct 

 liftuig upward and over to the opposite point of the compass. 

 Pins, with their heads pointing east, were inserted in the stems just 

 beneath the terminal flower head. Through all the variation in 

 •the direction of the curves, the heads remained unchanged in 

 direction. This proves it was not an uncoiling operation, but 

 -done as a purely ascending and descending act. 



Further, these observations show that the curvature proceeds at 

 night to the same extent as by day. Light, therefore, or the 

 attraction of the sun's rays, must be eliminated from the factors in 

 the work, especially as the evening curvature of one species is iu a 

 different direction from the other. So far as these observations 

 go, the cause of motion is still obscure. 



While these observations were in progi-ess, I noted on the even- 

 ing of September 5 that a large plant of Palafoxla linearis that 

 certainly had all its branchlets erect in the morning were beauti- 

 fully curved at 6 P.M., but they were in no particular direction of 

 the compass. The curv^ed branches were so rigid that they resisted 

 considerable force in the endeavor to straighten them. The next 

 •day at 7 A.M. they were perfectly straight. The observations 

 •were made daily till the lltli, with the same results, the only addi- 



