142 Macfarlane, The Sensitive Movements of some Flowering Plants. 



September 16 th. A clear, hot day, with uninterrupted 

 sunshine. Frequent Observation» made during the day essentially 

 agreed with those given above, so that it is unnecessary to repeat 

 the records. 



September 17 th. The day was warm on the whole, but 

 dull clouds greatly obscured the sun's rays tili 12 : 45. Thereafter 

 bright sunlight and cloud shade alternat ed tili sunset. No obser- 

 vations could be made tili 2 : 30, when the leaflets of plant 1 were 

 rellexed, those of 2 slightly so or flat, those of 3 were also flat; 

 those of 4 were inflexed 25—30°. From 2:50 tili 3: 15 heavy 

 white clouds passed over, and at 3 : 10 the leaflets of 4 had 

 almost recovered. Thereafter bright sunshine tili 3 : 50 caused 

 them again to elose about 20°. Clouds again came over, and at 

 4 p. in. plants 1, 2, and 3 were uncovered. 



When uncovered, the plants were left in position tili next 

 morning, but their relative periods of nictitropic movement were 

 watched. The results are curious, but I attach little importance 

 to them, tili supported by several sets of similar observations. 

 Instead of showing earlier nyctitropism than the exposed plants 

 which were fully three-fourths closed at 5 : 50, plants 1, 2 and 3 

 were at that time fully expanded. At 6 : 20 plant 1 had slightly 

 inflexed, 2 had inflexed 20°, 3 about 35°. Plant 4, which had 

 recovered its flat State about an hour before, was beginning to 

 close under the blue screen. 1t was then uncovered, and by 7 

 p. m. it and plant 3 were almost closed, but 1 and 2 only three- 

 fourths. At 8 all were shut. On a priori grounds, one might 

 have expected day-by-day a gradual return to the normal, in 

 plants 1 and 2. These fragmentary observations are given, however, 

 if only to stimulate research in the same line. 



While the above studies were in progress, experiments were 

 conducted to ascertain whether the paraheliotropic movement is 

 solely determined by changes in the pulvinus cells, or is due to 

 changes in the tissues of the leaflets that indirectly cause chan- 

 ges in the cells. Oltmanns' experiments by the use of a black 

 screen decided this point for Robinia * But the usually flat 

 position of leaflets when growing under the shade of trees decided 

 me to use narrow strips of oak leaf. On a warm day, with sun 

 temperature at 35.5° C, three strips, each about 2 m. m. in 

 width and 35 m. m. in length were cut out of a leaf of Quercus 

 nigra. Each weighed about O.Ollgramme. These were delicately 

 placed along the pulvini of 2 leaves on one plant, and of one 

 leaf on another, which had their leaflets inflexed 45 — 50o. In a 

 few minutes the leaflets had rexpanded so as to form an angle 

 only of 5 — 10°. Pieces of leaf were then placed as follows : 

 1) On the pulvini of the lower seven pairs of leaflets of a thirteen- 

 paired leaf, 2) on the upper eight pairs of a sixteen-paired leaf, 

 and 3) on the middle flve pairs of a seventeen-paired leaf. 



* Flora. 1892. p. 234. 



