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Show 114 PUL VINI OF COTYLEDONS. CUAP. II. without such aiel, is reduced to tho expansion of the cells not being followed by growth in the first case, and beino- so followed. in tho second case. b Dots were made with Indian ink along tho midrib of both pulvinated cotyledons of a rather olll soo<llinO' of Oxalis Valdiviana; their distances wore repeatedly measured with an eye-piece micrometer dnring 8i; days, and they did not exhibit tho least trace of increase. It is therefore almost certain that the pulviuus itself was not then growing. N evertholess, during this whole time and for ten days afterwards, these cotyledons rose vertically every night. In tho case of some seedlings raised from seeds purchased under the name of Oxalis jloribunda, tho cotyledons continued for a long time to move vertically clown at night, and the movement apparently depended exclusively on the pulvini, for their petioles were of nearly the same length in young, and in old seedlings which had produced true leaves. With some species of Ottssia, on the other hand, it was obvious without any measurement that the pulvinated cotyledons continued to increase greatly in length during some weeks; so that here the expansion of the cells of the pulvini nnd the growth of the petiole were probably combined in causing their prolonged periodic movements. It was equally evident that the cotyledons of many plants, not provided with pulvini, increased rapidly in length; and their periodic movements no doubt were exclu-sively due to growth. . . In accordance with the view that the penod1c movements of all cotyledons depend primarily on the expansion of the cells, whether or not followed by growth, we can understand the fact that there is but little difference in the kind or form of movement in the two sets of cases. This may be seen by com· CIIAP. II. PUL VINI OF COTYLEDONR. 115 paring the diagrams given in tho last chapter. Thus the movements of the cotyledons of Brassica oleracea and of Ipomrea cmn~lea, which are not provided with pulvini, are as complex as those of Oxalis and Cassia which are thus provided. The pulvinated cotyledons of some individuals of ll!nmosa pudica and Lotus Jacobmus made only a single oscillation, whilst those of other individuals moved twice up and down in the course of 24 hours; so it was occnsionnJly with the cotyledons of Cuc~~rbita ovifera, which arc destitute of a pulvinus. The movements of pulvinated coty leclons are generally larger in extent than those without a pulvinus; nevertheless some of the latter movecl through an angle of 90°. There is, however, one important difference iu the two sots of cases; the nocturnal movements of cotyledons without pulvini, for instance, those in tho Cruciform, Cucur1itacere, Githago, and Beta, never last even for a 'voelc, to any conspicuous degree. Pulvinated cotyledons, on the other hancl, continue to rise at night for a much longer period, even for more than a month, as we shall now show. But tho period no doubt depends largely on the temperature to which tho seedlings are exposed and their consequent rate of development. Oxalis Vuldiviana.-Somo cotyledons which had lately opened a?d were horizontal on March 6th at noon, stood at night vertiCally up; on the 13th tho first true leaf was formed, and was embraced at night by the cotyledons; on April 9th, after an interval of 35 days, six loaves were developed, and yet the cotyledons rose almost vertically at night. The cotyledons of another seedling, which when first observed had already produced a leaf, stood vertically at night and continued to do so for 11 additional days. After 16 days from the first observation tw.o loaves were developed, aud the cotyledons were still greatly raised at night. After ~1 days the cotyledons during the day were deflected beneath the horizon, but at night were raised 45° I :2 |