312 Schively — Contributions to the Life History of 



90 ; obtuse and acute angles have also been noted. Out 

 of seventy-five leaves upon eight plants, the petioles of 

 eleven showed obtuse angles, six, acute, and the remainder 

 were right angles. Upon one plant two different angles may 

 be observed ; usually, however, uniformity exists. Certain 

 leaves showing each of the angles were marked and 

 watched upon several successive nights ; each night the 

 customary noted angle was regularly assumed. There 

 seems to be no reason for this difference ; but in the numer- 

 ous sets of plants studied, it was always seen. The right 

 angle, then, appears to be the prevailing one. As the 

 normal leaf position showed an angle varying from 45 ° to 

 6o°, there would here be a fall of 45 ° to 30 . 



Darwin 11 states that the petiole may fall through about 57 . 

 From the facts given, he must have studied one which as- 

 sumed an obtuse angle. No others are mentioned by him. 

 Those which did assume this angle seemed to the writer 

 to fall much more than the number of degrees estimated 

 by Darwin; certainly 75 ° is nearer the correct amount. 



In the passage above referred to, the circumnutation of 

 the leaf was traced by Darwin 11 . He is not himself, satis- 

 fied with the method employed, but his object was, he 

 states, " to ascertain if the leaf moved after it had gone to 

 sleep." A diagram of his results is given, but they do not 

 give an exact idea of what may be observed during the night 

 hours. First, the apparatus used would seem to me to 

 have a deflexing effect upon the entire leaf. Secondly, it 

 records movements of the terminal leaflet only, and even 

 the results for it are questionable. Thirdly, his observa- 

 tions ceased at 10.50 p.m. What is to be seen after that 

 hour will be described presently. However, it may be 

 indicated that so great and varied is the activity of leaflets, 

 that no idea is given by the tracing nor by the description 

 in Darwin's work. 



The movements until 11 p.m. have already been de- 

 scribed. From that hour till daylight, leaflets are con- 

 stantly in motion. Observations were made every half- 



