314 Schively — Contributions to the Life History of 



no indications of movement being visible before 4.45. 

 Mimosa assumed day position about a half hour later than 

 Ampliicarpcea. 



Observations were made to ascertain what relation the 

 time of assuming nyctitropic position bore to the hour of 

 sunset. Until the early part of May, records were made 

 from plants in the green-house only ; after that time com- 

 parisons could be made with those growing in the Botanic 

 Garden. During the time the green-house was artificially 

 heated, the temperature frequently fell late in the after- 

 noon, and, as the final watering for the day occurred about 

 that time, the hygrometer record was high. 



Previous to April no data of value were obtained. Dur- 

 ing that month, upon clear, warm afternoons, the nycti- 

 tropic position was assumed about nine minutes before 

 sunset (6.24-6.54 p.m.). 



During May, ten to twelve minutes before sunset (6.55— 

 7.21 p.m.) was the general time. May, 1896, was a most 

 unfavorable month, as there were but few clear, warm days. 



After that — in June and July — plants in the green-house 

 were often completely nyctitropic, fifteen or twenty min- 

 utes before those in the garden, which quite often, although 

 showing indications of nyctitropic position for some min- 

 utes, did not assume it completely until sunset hour or a 

 minute or two before (7.30 p.m.). 



These differences may be attributed to the following cir- 

 cumstances : — the humidity of the green-house, and close- 

 ness of the air, and comparatively, the more rapid approach 

 of darkness, caused by shading of the green-house by certain 

 adjoining walls. In June the position of the sun was such 

 that these conditions were quite noticeable. Those out of 

 doors had the advantage of all the light at that time as 

 well as fresh air. 



Dark, rainy days caused rapid assuming of the nycti- 

 tropic position from thirty to fifty minutes previous to 

 sunset. 



On such days, the plants out of doors gave no exact 



