CHAP. VI. SLEEP OF COTYLEDONS. 299 



respect to the sleep of cotyledons. In certain cases, 

 the cotyledons whilst young diverge during the day to 

 only a very moderate extent, so that a small rise at 

 night, which we know occurs with the cotyledons of 

 many plants, would necessarily cause them to assume 

 a vertical or nearly vertical position at night ; and in 

 this case it would be rash to infer that the movement 

 was effected for any special purpose. On this account 

 we hesitated long whether we should introduce several 

 Cucurbitaceous plants into the following list ; but from 

 reasons, presently to be given, we thought that they 

 had better be at least temporarily included. This 

 same source of doubt applies in some few other cases ; 

 for at the commencement of our observations we did 

 not always attend sufficiently to whether the cotyle- 

 dons stood nearly horizontally in the middle of the day. 

 With several seedlings, the cotyledons assume a highly 

 inclined position at night during so short a period of 

 their life, that a doubt naturally arises whether this 

 can be of any service to the plant. Nevertheless, in 

 most of the cases given in the following list, the coty- 

 ledons may be as certainly said to sleep as may the 

 leaves of any plant. In two cases, namely, with the 

 cabbage and radish, the cotyledons of which rise almost 

 vertically during the few first nights of their life, it 

 was ascertained by placing young seedlings in the 

 klinostat, that the upward movement was not due to 

 apogeotropism. 



The names of the plants, the cotyledons of which 

 stand at night at an angle of at least 60 J with the 

 horizon, are arranged in the appended list on the same 

 system as previously followed. The numbers of the 

 Families, and with the Leguminosre the numbers of 

 the Tribes, have been added to show how widely 

 the plants in question are distributed throughout the 



