Macfarlane, The Sensitive Movenients of some Flowering Plants. 143 



Expansion of the partially covered leaflets followed, and cansed a 

 strikiug appearance in the leaves. That the weight of the oak 

 Jeaf did not cause the movement, was proved by substituting 

 strips of mica of like size, each weighing about 0.079 gramme. 

 No visible movement followed. 



Careful observations were then made on Cassia nicbitans and 

 C. chamaecrüta to ascertain how soon, after shading, the change 

 of position is evident. In the former species P/s minutes, and in 

 the latter 2 l U — 2 5 /s minutes sufliced according to the age of the 

 leaf. The relative rapidity of movement thus established is a 

 pretty exact index to the relative sensitivity of the species. Thus 

 Strojjhoxtyles angulosa which feebly responds to mechanical 

 Stimuli, and only slowly though markedly responds to sun Stimuli, 

 does not, when shaded, re-expand under 25 — 30 minutes. 



Attempts were made with the leaves of Cassia nictitam to 

 ascertain whether continuous exposure to bright light would in jure 

 them. Attached leaves were enclosed at 11.30 a. m. on a warm day 

 between thin glass slips that pressed lightly against them. Within 

 ten minutes minute droplets of liquid appeared over the upper 

 and under surfaces of the leaflets, and this liquid steadily increased 

 in amount, until after fifty-four hours, the leaves werequite drenched. 

 The experiments were unavoidably stopped at this stage, but none 

 of the leaves used had quite lost their sensitivity, though they had 

 a very flaccid and slightly discolored appearance when left a few 

 hours after. Prolonged and varied experiments are needed here. 



Cassia Tora. 



On September 17 th at 5:30 p. m. young vigorous plants 

 in pots were placed under the colored screens previously used. 

 The succeeding day was wet and the sky was dense. The leaflets 

 on all of the plants were fully expanded when examined at 9 : 15 

 a. m., but further notes could not be made until the succeding 

 day at 4 p. m., when the leaflets were expanded. At 4 : 15 plant 

 1 began to show nyctitropism, at 4 : 40 plant 2, at 5 : 20 plant 3, 

 and at 5 : 50 plant 4. Further observations could not be made 

 tili the following date : 



September 21s t. The day was clear and sunlight unin- 

 terrupted, though the temperature was not high. At 8 : 45 a. m. 

 the leaflets in all were fully expanded. At 11 : 10 two exposed 

 control plants showed leaflets contracted by paraheliotropism 

 through 40 — 45°. The leaflets of 1 were almost fully expanded; 

 those of plant 2 were mostly flat, though a few were reflexed. 

 The leaflets of plant 3 were inflexed through 25 — 30°, and those 

 of plant 4 through 50°. This condition persisted tili 3 : 40 when 

 the leaflets of 4 began to re-expand; by 5:20 they were flat. 

 At 5 : 30 plants 1, 2 and 3 showed difTerent degrees of nyctitro- 

 pism, while 4 had leaflets expanded. At 6 : 30 plants 1 and 2 

 were closed, 3 was almost closed, and 4 had closed through 40°. 

 At 7 : 45 plant 3 was closed, and 4 had moved through 75°. By 

 9 : 30 all had shut. 



