14^ 



INCLINATION' OF PLAINTS TOWARD THE LieHT» 



XV. 



Remarks on the Inclination of the Stems of Plants toward the 

 Light : by M. Decandolle *. 



Inclination of 

 stems of plants 

 toward the 

 light. 



not from voli- 

 tion or instinct, 



but known 

 laws of vege- 

 Utioa. 



Etiolation, 



rot a general 

 but topical 

 ^kffeclion. 



Oi 



Various de- 

 grees oi it. 



F all the phenomena that living veo^etables exhibit, there 

 are few appear so extraordinarj', as the energy and constancy 

 with which their stems incline toward the light. Not only 

 has no explanation been given hitherto of this fact' by aTty 

 physiologist, but writers have even been found, who, more 

 of the poet than of the naturalist, have ascribed this ten- 

 dency to some kind of instinct or volition in plants. I 

 think I can prove in a few words, that it is a simp^le and ne- 

 cessary consequence of the known laws of vegetation^ Wiiat 

 I have to say in this respect will even apfiear of so elemefttkiry 

 a nature, that every one will be surprised not to have met 

 with in all books : and that I shall be pardoned'for' writing 

 it only on account of the wanderings, into which some have 

 gone on the subject. 



Every one knows^ that the statc^ of* silvery Whiteness 'and 

 extraordinary elongation, acquired by plantsthat gr6w"' in 

 darkness, is designated by the term etiolation. AU\Vh'6'h^Vfe 

 studied this disease know, that it is not a general disease*, 

 but a local affection ; as I have satisfied myself by direct 

 experiments. If we expose to the light of day an etiolated 

 plant, in two days it will«cqoire a-^reen colour perceptibly 

 similar to that of plants, which have grown in open day- 

 light. If we expose to the light one part of the plant, be 

 it leaf or branch, this [)art alone will become green. If we 

 cover any part of a leaf with an opake substance, this place 

 will remain white, while the rest becomes green. The 

 whiteness of the inner leaves of cabbages is a partial etio- 

 lation, atid a thousand other examples might easily be 

 quoted. Etiolation therefore is certainly a local, and not 

 a general disease. 



On the othfer hand it is equally certain, that between 

 complete etiolation and complete verdure evel'vpos^ibfe in- 

 tlertcediate degree exists, determined by the intertsityof ^he 



• M€tn, de la Soc. d'Aroueil, vol. II, p. 104. 



light. 



