CHAP. VI. USE OF SLEEP MOVEMENTS. 293 



sun-dial close by), and 8 of these leaves were killed. Of the free 

 leaves (those on the trailing branches not being considered), a 

 good many were killed, but their number, compared with the 

 uninjured ones, was small. Finally, taking the three trials 

 together, 24 leaves, extended horizontally, were exposed to the 

 zenith and to unobstructed radiation, and of these 20 were 

 killed and 1 injured ; whilst a relatively very small proportion 

 of the leaves, which had been allowed to go to sleep with their 

 leaflets vertically dependent, were killed or injured. 



The cotyledons of several plants were prepared for trial, but 

 the weather was mild and we succeeded only in a single instance 

 in having seedlings of the proper age on nights which were 

 clear and cold. The cotyledons of 6 seedlings of Mimosa pudica 

 were fastened open on cork, and were thus exposed for 1 h. 45 m. 

 to a clear sky, with the temperature on the surrounding ground 

 at 29 F. ; of these, 3 were killed. Two other seedlings, after 

 their cotyledons had risen up and had closed together, were 

 bent over and fastened so that they stood horizontally, with the 

 lower surface of one cotyledon fully exposed to the zenith, and 

 both were killed. Therefore of the 8 seedlings thus tried 5, or 

 more than half, were killed. Seven other seedlings, with their 

 cotyledons in their normal nocturnal position, viz., vertical and 

 closed, were exposed at the same time, and of these only 2 were 

 killed.* Hence it appears, as far as these few trials tell anything, 

 that the vertical position at night of the cotyledons of Mimosa 

 pudica protects them to a certain degree from the evil effects of 

 radiation and cold. 



Concluding Remarks on the Radiation from Leaves 

 at Night. We exposed on two occasions during the 

 summer to a clear sky several pinned-open leaflets 

 of Trifolium pratense, which naturally rise at night, 

 and of Oxalis purpurea, which naturally sink at night 

 (the plants growing out of doors), and looked at 



* We were surprised that It may be added that seedlings of 



young seedlings of so tropical a the Indian Cassia pubescens were 



plant as Mimosa pudica were able exposed for 1 h. 30 m. to a clear 



to resifet, as well as they did, ex- sky, with the temp, on the sur- 



posure for 1 hr. 45 m. to a clear rounding ground at 2 C., and 



Kky, the temperature on the sur- they were not in the least injured, 

 rounding ground being 29 F. 



