PALMS. 21 



cd ;* but soon displays the most vigorous powers of vegetation. Its 

 growth, inflorescence, and progress towards maturity are indicated 

 by the decay and fall of the leaves which had hitherto protected it. 

 The age of a palm-tree, or rather the number of times tliat it has 

 fructified, or become crowned with fresh leaves, is calculated by the 

 number of woody circles which are found marked on the s«^em. Its 

 power of lasting seems to have no other limits than the resistance 

 which the base offers to the weight it supports. In these colossal 

 trees, a sensible diminution in the diameter of the stem is often per- 

 ceptible towards the top, and in most of the species 't .'s a fact 

 equally well proved, that the fruit decreases in quantity when they 

 have attained a certain epoch of their existence. In the cocoa-nut 

 tree {lodicen cocus nucifera) the period of this decrease shows itself 

 at about the age of tiiirty years, although this tree continues to bear 

 for nearly a century. f 



The leaves, the forms of which are so various, present however 

 the greatest analogy in their organization : the green membranous 

 substance of which they are almost entirely composed, is an exten- 

 sion of the parenchyma ; the envelope which covers them answers 

 to the epidermis. 



It is in the leaves that the sap is subjected to the action of the 

 atmosphere ; it is there concentrated and peculiarly modified. Ac- 

 cording to the position of leaves upon the plant, their under sides, 

 or those turned towards the ground, are distinguished from their 

 upper sides which meet the light from above. 



The upper side of the leaf is covered with a thick and f-equently 

 shining epidermis ; this epidermis is sometimes endued with a sub- 

 stance rich in silicious matter, as in rushes. In the Steppes of 

 South America I observed a tree, called Chapparal, the leaves of 

 which are so highly silicious, that they are used for polishing metals. 

 Generally speaking, the covering of the upper surface of leaves is a 

 matter which is something of the nature of wax or resin. The 

 epidermis which covers the lower surface is formed in njost cases 

 '^f a very thin, rough membrane, full of cavities and frequently cov- 

 ered with hairs or down. 



The appearance and position of the leaves are not the same du- 

 ring the day and night. In the dark, simple leaves incline to fold 

 up; in compound leaves, as in those of the acacia and sensitive 

 plant, the same thing is still more marked ; the effect can even be 

 produced at will. If during the day a sensitive })lant is placed in a 

 dark room, the leaves immediately close ; on lighting the room«ven 

 with candles, they open again as if under the influence of the solar 

 light ;J Linnffius, who first paid attention to this class of plienome- 

 na, admits that plants in the absence of light experience a sort of 

 sleep. 



* This bud, in certain species of palm-trees, is sought after as food, and is often 

 spoken of as the cabbage of the prslm-tree. 



t Infornrition communicated by Mr. Codazzi. The trunk of certain spec.es of palm- 

 trees shows an enlargement towards the middle of its height, as in the palma harriffonc 

 of Choco. 



% Observation of M. de Candolle. 



