. The power of movement in plants. Plants; Botany. Chap. II. PULYINI OF COTYLEDONS. 113 cushion, or joint (as this organ has been variously called), like that with which many leaves are provided. It consists of a mass of small cells usually of a pale colour from the absence of chlorophyll, and with its outline more or less convex, as shown in the annexed figure. In the case of Oxalis sensitiva two-thirds of the petiole, and in that of Mi- mosa pudica, apparently the whole of the short sub- petioles of the leaflets have been converted into pulvini. With pulvinated leaves ( those provided wi
. The power of movement in plants. Plants; Botany. Chap. II. PULYINI OF COTYLEDONS. 113 cushion, or joint (as this organ has been variously called), like that with which many leaves are provided. It consists of a mass of small cells usually of a pale colour from the absence of chlorophyll, and with its outline more or less convex, as shown in the annexed figure. In the case of Oxalis sensitiva two-thirds of the petiole, and in that of Mi- mosa pudica, apparently the whole of the short sub- petioles of the leaflets have been converted into pulvini. With pulvinated leaves ( those provided with a pul- vinus) their periodical move- ments depend, according to Pfeffer,* on the cells of the pulvinus alternately expand- ing more quickly on one side than on the other; whereas the similar movements of leaves not provided with pul- vini, dbpend on their growth being alternately more rapid on one side than on the As long as a leaf provided with a pulvinus is young and continues to grow, its movement depends on both these causes combined ;| and if the view now held by many botanists be sound, namely, that growth is always preceded by the expan- sion of the growing cells, then the difference between the movements induced by the aid of pulvini and. Oxalis rosea: longitudinal section of a pulvinus on the summit of the petiole of a cotyledon, drawn with the camera luciJa, magnified 75 times: p, p^ pe- tiole ; /, fibro-vascular bundle ; 6,6, commencement of blade ol cotyledon. * 'Die Perioclische Bewegun- gcn der Bliittorgane,' 1875. t Batalin,'Flora,'Oct. 1st, 1873 t Pfeffer, ibid. p. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Darwin, Charles, 1809-1882; Darwin, Francis, Sir, 1848-1925. New York, Appleton
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