S^O Action of the Yellow Rai/s of Light on Vegetation. 



mentioned that " turnep seeds were sown, and every grain 

 germinated in the yellow and red rays — the greenest plants 

 were found in yellow light." This is directly in opposition to 

 Mr. Hunt, who found in his experiments, " that the yellow 

 and red rays destroy the vital principle in the seed." From 

 this circumstance there appears to be either some error on the 

 part of one of these gentlemen, or that some circumstances 

 have affected the experiments of the one which have not in- 

 fluenced those of the other. Dr. Gardner supposes the dif- 

 ference to have arisen from the earth being rapidly dried in 

 the experiments of Mr. Hunt, which he considers sufficient 

 to retard or destroy germination. 



It appears to me that Dr. Gardner has overlooked one cir- 

 cumstance in his experiments which seem strongly to militate 

 against the production of chlorophylle by yellow light, or else 

 to show that there is some error either in his experiments or 

 in the account which he has published of them ; this is, that 

 the seeds of vegetables germinate most rapidly in yellow light. 

 In the paragraph referred to he merely states this in general 

 terms, whilst in giving the results of the other experiments in 

 detail he mentions that seedling plants were operated upon. 

 Now we know, both from the observations of Ingenhousz and 

 Sennebier, as well as from daily experience, that the absence 

 of solar light is one of the conditions almost necessary for 

 the germination of seed, and consequently we should not ex- 

 pect that ray in which the maximum of light is found to faci- 

 litate germination, but on the contrary, as in Mr. Hunt's ex- 

 periments, to retard it. 



This, however, is not the only objection to which this state- 

 ment is liable, for if the yellow ray be the operating cause by 

 which carbonic acid is decomposed and chlorophylle produced, 

 we should also expect that, so far from assisting in germination, 

 it would exercise a highly injurious influence. We know that the 

 presence of oxygen is necessary for the vegetation of seeds, and 

 also that this oxygen is absorbed, and by uniting with a por- 

 tion of the carbon in the seed reappears in the form of carbonic 

 acid, a process the opposite of that which takes place when 

 chlorophylle is produced. This change is required in order 

 that the amylaceous principle in the seed may be rendered suf- 

 ficiently soluble for the support of the germ, previous to its 

 being able to obtain the requisite nutriment from the soil ; so 

 that, if the decomposition of carbonic acid be owing to the 

 yellow ray, this same ray ought to be the last to produce any 

 effect on the germination of seeds. It appears moreover that 

 seeds as well as fully developed vegetables possess the power 

 when deprived of light of absorbing oxygen and evolving car- 



