262 CIECUMNUTATION OF LEAVES. CnAr. I\ 



and 3 were so young that their epinastic growth 

 which serves to bring them down into a horizontal 

 position, overpowered every other kind of movement. 

 In only one genus, Cannabis, did the leaves sink in 

 the evening, and Kraus attributes this movement to 

 the prepotency of their epinastic growth. That the 

 periodicity is determined by the daily alternations 

 of light and darkness there can hardly be a doubt, as 

 will hereafter be shown. Insectivorous plants are 

 very little affected, as far as their movements are con- 

 cerned, by light ; and hence probably it is that their 

 leaves, at least in the cases of Sarracenia, Drosera, and 

 DionEea, do not move periodically. The upward move- 

 ment in the evening is at first slow, and with different 

 plants begins at very different hours ; — with Glaucium 

 as early as 11 a.m., commonly between 3 and 5 p.m., 

 but sometimes as late as 7 p.m. It should be observed 

 that none of the leaves described in this chapter 

 (except, as we believe, those of Lupinus speeiesus) 

 possess a pulvinus; for the periodical movements of 

 leaves thus provided have generally been amplified 

 into so-called sleep-movements, with which we are not 

 here concerned. The fact of leaves and cotyledons 

 frequently, or even generally, rising a little in the 

 evening and sinking in the morning, is of interest as 

 giving the foundation from which the specialised sleep- 

 movements of many leaves and cotyledons, not pro- 

 vided with a pulvinus, have been developed. The 

 above periodicity should be kept in mind, by any one 

 considering the problem of the horizontal position oi 

 leaves and cotyledons during the day, whilst illumi- 

 nated from above. 



