OF PLANTS. ^ 197 



from the concave side of the cup. What is called also the 

 sleep* of plants, is the leaves of petals disposing themselves 

 in such a manner as to shelter the young stems, buds, or 

 fruit. They turn up, or they fall down, according as this 

 purpose renders either change or position requisite. In 

 the growth of corn, whenever the plant begins to shoot, the 

 two upper leaves of the stalk join together, embrace the 

 ear, and protect it till the pulp has acquired a certain de- 

 gree of consistency. In some water plants, the flowering 

 and fecundation are carried on within the stem, which af- 

 terwards opens to let loose the impregnated seed.t The 

 pea or papilionaceous tribe enclose the parts of fructifica- 

 tion within a beautiful folding of the internal blossom, 

 sometimes called, from its shape, the boat or keel ; itself 

 also protected under a penthouse formed by the external 

 petals. This structure is very artificial ; and, what adds to 

 the value of it, though it may diminish the curiosity, very 

 general. It has also this further advantage, (and it is an 



*The periodical change in the direction of leaves, which has been 

 called the " Sleep of Plants," is undeniably connected with the stimu- 

 lating operation of light. It is established, that during the clear 

 light of the sun, the leaves become erect, and move their upper sur- 

 face to the light, whilst, on the contrary, during the absence of light 

 they either hang dovvnvt'ards, and turn to the horizon, or they take an 

 upright position, so that the under surface of the leaves is turned 

 more outward. On account of this particular position of what has 

 been called " Sleeping Plants," we cannot properly ascribe this direc- 

 tion to sleep, because the leaves do sometimes even raise themselves 

 during this state with greater energy, and press upon the stem or leaf- 

 stalk, ibr the purpose of turning their lower surface outwards. This 

 change is much rather, therefore, the consequence of the contest be- 

 tween the activity of the plant, and the great activity of nature. 

 This change is the more evident, and the sleep of leaves the more 

 striking, the finer and more compounded the organization of the leaves 

 are. We hence most frequently observe it in the pinnated leaves of 

 leguminous plants, although also in some others, as in atriplex. 



That an internal and self-dependent activity is to be taken into ac- 

 count in this sleep of plants, is plain from the fact that this sleep does 

 not equally follow fromashort withdrawing of the light, but only from 

 its complete and long-continued removal ; as also from this other cir- 

 cumstance, that leaves fall asleep or awake at fixed hours, whether 

 the sky be serene or troubled, exactly as happens with regard to ani- 

 mals. Other stimuli, too, and especially heat, have a great influence 

 upon this phenomenon, because, in the cold, leaves awaken later 

 and fall more easily asleep, notwithstanding the influence of light. 

 Vide Elements of the Philosophy of Plants, by Decandalle. 



Paxton. 



+ Phil. Trans, part ii. 1796, p. 502. 



