THE MOVEMENTS AND HABITS OF PLANTS. 25 



or quite vertically at night. Therefore the apex, or the 

 base, or either lateral edge, may be directed toward the 

 zenith. Moreover, the upper surface of each leaf, and 

 more especially of each leaflet, is often brought into 

 close contact with that of the opposite one ; and this is 

 sometimes effected by singularly complicated movements. 

 This fact suggests that the upper surface requires more 

 protection than the lower one. For instance, the ter- 

 minal leaflet in trifolium, after turning up at night so as 

 to stand vertically, often continues to bend over until the 

 upper surface is directed downward, while the lower sur- 

 face is fully exposed to the sky ; and an arched roof is 

 thus formed over the two lateral leaflets, which have their 

 upper surfaces pressed closely together. Here we have 

 the unusual case of one of the leaflets not standing verti- 

 cally, or almost vertically, at night. 



Considering that leaves in assuming their nyctitropic 

 positions often move through an angle of 90° ; that the 

 movement is rapid in the evening ; that in some cases it 

 is extraordinarily complicated ; that with certain seed- 

 lings, old enough to bear true leaves, the cotyledons move 

 vertically upward at night, while at the same time the 

 leaflets move vertically downward ; and that in the same 

 genus the leaves or cotyledons of some species move 

 upward, while those of other species move downward — 

 from these and other such facts, it is hardly possible to 

 doubt that plants must derive some great advantage from 

 such remarkable powers of movement. 



SELF-PEOTECTION DUBING SLEEP. 



p m 284 ^ e ^ ac ^ ^a-t the leaves of many plants 



place themselves at night in widely different 



positions from what they hold during the day, but with 



