Chap. VI. SLEEP OP COTYLEDONS. 297 



immediately feel relief; and this is evidently an 

 analogous, though, reversed, case. These several facts 

 — in relation to leaves pinned close to or a little above 

 the cork-supports^to their tips projecting beyond it — 

 and to the leaves on branches kept motionless — seem 

 to ,us curious, as showing how a difference, apparently 

 trifling, may determine the greater or less injury of 

 the leaves. We may even infer as probable that the 

 less or greater destruction during a frost of the leaves 

 on a plant which does not sleep, may often depend on 

 the greater or less degree of flexibility of their petioles 

 and of the branches which bear them. 



Nyctitkopic oe Sleep Movements of Cotyledons. 



We now come to the descriptive part of our work, 

 and will begin with cotyledons, passing on to leaves 

 in the next chapter. We have met with only two 

 brief notices of cotyledons sleeping. Hofmeister,* 

 after stating that the cotyledons of all the observed 

 seedlings of the Caryophyllese (Alsinese and Silenese) 

 bend upwards at night (but to what angle he does not 

 state), remarks that those of Stellaria media rise up so 

 as to touch one another ; they may therefore safely be 

 said to sleep. Secondly, according to Eamey, t the 

 cotyledons of Mimosa pudica and of Clianihus Bam- 

 fieri rise up almost vertically at night and approach 

 each other closely. It has been shown in a previous 

 chapter that the cotyledons of a largo number of 

 plants bend a little upwards at night, and we hero 

 liave to meet the difficult question at what inclinatioji 

 may they be said to sleep? According to the view 

 ffhich we maintain, no movement deserves to be called 



• ' Die Lehre von der Pflanzenzelle,' 18C7, p. 327 

 t 'Ailansonia,' March 10th, I8G9. 



