14 Dr. Gardner on the Action of Light upon Vegetables. 



The ordi nates are from the table. Fraunhofer's estimates are 

 indicated by a bold line, Dr. Draper's by dots, and my own by 

 an interrupted line, fig. 1, 



Fig. 1. 



<&0 R ■ . S H <$ 



Had more points in these figures been determined, there is no 

 doubt they would have coincided precisely. It is not to be for- 

 gotten, that these results were obtained in places many hundred 

 miles apart. They determine, what hitherto has only been con- 

 jectured, that the greening of plants, and decomposition of car- 

 bonic acid, are produced by the same agent — which is also the 

 active imponderable in producing vision — a phenomenon in no 

 way similar, as suggested by M. Moser, to the change of Da- 

 guerre's plate, which is a tithonic action. The dependence of 

 the depth of green color in foliage, upon brilliant light, is also 

 shown. The statements of travellers, in respect to tropical vege- 

 tation, confirms this conclusion. 



(38.) Chlorophyl, the body generated in the yellow leaflets of 

 plants, raised in darkness, by the action of light, is a hydrocarbon, 

 of the nature of wax. Whether it be produced by decomposition 

 of carbonic acid, or be the yellow matter, or some other substance, 

 as dextrine, already present in the leaf, which has suffered deox- 

 idation, is altogether unknown. The latter view, applied to the 

 formation of oils, and fats in animals, by Liebig, is probably cor- 

 rect — by adopting it, we are relieved from all difficulty in regard 



