374 MODIFIED CIBCUMNUTATION. CHAP. VII. 



Owing to this movement to the leaves being folded and to 

 the petioles rising, the whole plant is as much more compact at 

 night than during the day, as a fastigiate Lombardy poplar is 

 compared with any other species of poplar. It is remarkable 

 that when our plants had grown a little older, viz., to a height 

 of 2 or 3 feet, the petioles did not rise at night, and the midribs 

 of the folded leaves were no longer bent back along one side of 

 the petiole. We have noticed in some other genera that the 

 petioles of very young plants rise much more at night than do 

 those of older plants. 



Tamarindus Indica (Tribe 16). The leaflets approach or 

 meet each other at night, and are all directed towards the apex 

 of the leaf. They thus become imbricated with their midribs 

 parallel to the petiole. The movement is closely similar to 

 that of Hsematoxylon (see former Fig. 153), but more striking 

 from the greater number of the leaflets. 



Adenanthera, Prosopis, and Neptunia (Tribe 20). With Ade- 

 nantkera pavonia the leaflets turn edgeways and sink at night. 

 In Prosopis they turn upwards. With Neptunia oleracea the 

 leaflets on the opposite sides of the same pinna come into 

 contact at night and are directed forwards. The pinnae them- 

 selves move downwards, and at the same time backwards or 

 towards the stem of the plant. The main petiole rises. 



Mimosa pudica (Tribe 20). This plant has been the subject of 

 innumerable observations; but there are some points in rela- 

 tion to our subject which have not been sufficiently attended 

 to. At night, as is well known, the opposite leaflets come into 

 contact and point towards the apex of the leaf ; they thus be- 

 come neatly imbricated with their upper surfaces protected. The 

 four pinnae also approach each other closely, and the whole leaf 

 is thus rendered very compact. The main petiole sinks down- 

 wards during the day till late in the evening, and rises until 

 very early in the morning. The stem is continually circumnu- 

 tating at a rapid rate, though not to a wide extent. Some very 

 young plants, kept in darkness, were observed during two days, 

 and although subjected to a rather low temperature of 57 59 F., 

 the stem of one described four small ellipses in the course of 

 12 h. We shall immediately see that the main petiole is like- 

 wise continually circumnutating, as is each separate pinna and 

 each separate leaflet. Therefore, if the movement of the apex 

 of any one leaflet were to be traced, the course described would 

 be compounded of the movements of four separate parts. 



