124 DISTURBED PERIODIC MOVEMENTS. Chap. II. 



For instance, the cotyledons of Beta vulgaris, Solanum. lyeoper- 

 sicum, Cerinthe major, and Liipinus luteus, when placed in dark- 

 ness, moTed down during the afternoon and early night, instead 

 of rising as they would have done if they had been exposed tc 

 the light. All the individuals of the Solanum did not behave 

 in the same manner, for the cotyledons of one circumnutated 

 about the same epot between 2.30 and 10 p.m. The cotyledons 

 of a seedling of Vxalis corniculata, which was feebly illuminated 

 from above, moved downwards during the first morning in the 

 normal manner, but on the second morning it moved upwards. 

 The cotyledons of l.otits Jacohceus were not affected by 4 h. of 

 complete darkness, but when placed under a double skylight 

 and thus feebly illuminated, they quite lost their periodical 

 movements on the third morning. On the other hand, the 

 cotyledons of Cucurlita ovifera moved in the normal manner 

 during a whole day in darkness. 



Seedlings of Gilhago segetum were feebly illuminated from 

 above in the morning before their cotyledons had expanded, and 

 they remained closed for the next 40 h. Other seedlings were 

 placed in the dark after their cotyledons had opened in the 

 morning and these did not begin to close until about 4 h. had 

 elapsed. The cotyledons of Oxalis rosea sank vertically down- 

 wards after being left for lb. 20m. in darkness; but those of 

 some other species of Oxalis were not affected by several hours 

 of darkness. The cotyledons of several species of Cassia are 

 eminently susceptible to changes in the degree of light to which 

 they are exposed : thus seedlings of an unnamed S. Brazilian 

 species (a large and beautiful tree) were brought out of the hot- 

 house and placed on a table in the middle of a room with two 

 north-east and one north-west window, so that they were fairly 

 well illuminated, though of course less so than in the hot-house, 

 the day being -moderately bright; and after 36 m. the cotyledons 

 which had been horizontal rose up vertically and closed together 

 as when asleep ; after thus remaining on the table for 1 h. 13 m. 

 they began to open. The cotyledons of young seedlings of another 

 Brazilian species and of C. negleda, treated in the same manner, 

 behaved similarly, excepting that they did not rise up quite so 

 much : they again became horizontal after about an hour. 



Here is a more interesting case : seedlings of Cassia tora in 

 two pots, which had stood for some time on the table in the 

 room just described, had their cotyledons horizontal. One pot 

 was now exposed for 2 h. to dull sunshine, and the cotyledons 



