INCLINATION Ot' PLANTS TOWARDS THE LIGHT* J^5 



light.. Of this any one may easily satisfy himself, by at-» 

 tending to the colour of a plant exposed to the full day- 

 light ; it exhibits in succession all the degrees of verdure* 

 I had already seen the sahie phenomenon in a particular Etiolated 



manner, by exposina etiolated plauts to the light of lamos. F'^f'^s exposed 



•^ ^ " . ^. =■ 'to artificial 



In these experiments (inserted in vol. I, of the Mtm. des hghu 



Sav-ans etravgers) 1 not only saw the colour come on gra- 

 dually according to the continuance of the exposure to light j 

 but I satisfied myself, that a certain intensity of permanent 

 light never gives to a plant more than a certain degree of 

 colour. The same fact readily shows itself in nature, when 

 we examine the plants that grow under shelter or in forests, 

 or when we examine in succession the state of the leaves, 

 that form the heads of cabbage;^ 



Now let us examine the state of a plant, that is not Plants not 



equally enlightened on all sides, as we see them in forests; ®^"^|'y ^^' 



. . posed to light 



and still better in plants cultivated in hothouses, or in com- in forests, hot 



mon rooms. That part of the stalk which is exposed to the ^°"*«^'» *^^ 



. . . rooms, 



least light must necessarily be a little more etiolated than 



the other ; consequently it must elongate itself a little more, 



while the fibres on the side next the light must become on 



the contrary a little mure short and stiff. But it is evident, incline to th« 



that this inequality of elongation between the fibres of the ''S'^^ {i""^"! 



. ^ . , ' ", , . , , . partial etio- 



two opposite side;* cannot take place without the extremity lation. 



of the stalk tending to incline toward the side where the 

 fibres are shortest, that is to say, on the side next the light. 



Thus it appears, if this theory be true, that the energy, This incJini' 

 with which plants incline themselves toward the light, must "^" proper- 

 . 1.1- ix r ^u 1- i_^ L ■ ^ionh\ to the 



be proportional to the inequality ot the light they receive degree of the 



on opposite sides, and to the greater or less propensity to "ff'^ction. 



etiolation, that each plant, or part of a plant, possesses, in 



conseqae-ace of its structure. This. I shall proceed to prove 



by facts, most of them,^ it is true, already known, but which 



will be so many coAfirmations of my hypothesis. 



The parts of plants liable to etiolation alone possess this Only parts of 



tendency to incline toward the light. Of this any one may P'fn's hable to 



. „ , . ,„ , . . , ' , , ,. ' , , etiolation vn- 



satisty himselt, by examining the branches directed toward cllne toward 



the windows in a greenhouse not well lighted. He will find, ^^' light. 



that they are always the young shoots, capable of emitting 



oxigen gas, that direct themselves tpward the light ; and 



Vol. XXX .—Oct. 1811. L that 



