CHAP. II. PULVINI OF COTYLEDONS. 115 



paring the diagrams given in the last chapter. Thus 

 the movements of the cotyledons of Brassica oleracea 

 and of Ipomoea cserulea, 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 Mimosa pudica and Lotus 

 Jacobseus made only a single oscillation, whilst those 

 of other individuals moved twice up and down in the 

 course of 24 hours ; so it was occasionally with the 

 cotyledons of Cucurbita ovifera, which are destitute of 

 a pulvinus. The movements of pulvinated cotyledons 

 are generally larger in extent than those without a 

 pulvinus; nevertheless some of the latter moved 

 through an angle of 90. There is, however, one 

 important difference in the two sets of cases; the 

 nocturnal movements of cotyledons without pulvini, 

 for instance, those in the Cruciferae, Cucurbitaceae, 

 Githago, and Beta, never last even for a week, to any 

 conspicuous degree. Pulvinated cotyledons, on the 

 other hand, continue to rise at night for a much 

 longer period, even for more than a month, as we 

 shall now show. But the period no doubt depends 

 largely on the temperature to which the seedlings are 

 exposed and their consequent rate of development. 



Oxalis Valdiuiana. Some cotyledons which had lately opened 

 and were horizontal on March 6th at noon, stood at night ver- 

 tically up ; on the 13th the first true leaf was formed, and was 

 embraced at night by the cotyledons ; on April 9th, after an in- 

 terval of 35 days, six leaves were developed, and yet the coty- 

 ledons rose almost vertically at night. The cotyledons oi 

 another seedling, which when first observed had already pro- 

 duced a leaf, stood vertically at night and continued to do so for 

 11 additional days. After 16 days from the first observation 

 two leaves were developed, and the cotyledons were still greatly 

 raised at night. After '21 days the cotyledons during the day 

 were deflected beneath tlie horizon, but at night were raised 4 S 



