INFLUENCE OF SOLAR RAYS ON THE GROWTH OF PLANTS. 29 
be maintained under all the circumstances, yet if tlie red rays arc obstructed, 
flowers will not form. It is therefore evident that this verj’ remarkable pro¬ 
perty must depend upon some function peculiar to this class of rays. The 
researches of Sir John Herschel, Dr. Draper, M. Claudet and myself on 
the artion of the rays of the spectrum on photographic preparaliotjs, must 
materially assist us in explaining tliis phtenomenon. 
Sir John Herschel (Philosophical Transactions, vol. cxxxi. 18^0) has 
shown that the red rays iu some cas« exalt the oxidation of a silver salt j 
that they exert a protective power, and even prevent the darkeniug of puiHT 
covered with chloride of silver under the influence of diffused licht Hleport 
of the British Association, 1839). 
In the Philosophical Magazine, vol. xvi. K. S. p. 272-3, I liave described 
several experiments, which prove not merely the protecting power of this 
red ray. but a power of producing the closer combiimtlon of Uie chemical 
elements of a compound exposed to its influence. More rcrenilv Dr. Draper 
(Philosophical Magazine, 1846), and l\f. Claudet. who communicated his 
experiments to the Meeting of the British Association at Oxford, an abstract 
of wiiich appears in the pre'seot volume, have shown that this class of rays 
does not merely protect the chemical compound from any change, but (Imt 
after the suns rays have produced a cljange, tiiey have the power of again 
restoring the compound to its original condition. 
Ail these expeiitneuts have been repeated with many modifications, and 
partictilarJy the influence of this class of rays on growing ainl dead vegetable 
matter has been particularly observed. 
Leaves inspire carbonic acid and give out oxygen. It has bee'll shown by 
Pnestley, Scheelc, and Ingctiliousz, that flowers eonsiiino much more oxygen 
than any other part of tho growing plant. Suussure has shown that flowers 
will not be developed without oxygen ; that, so far from giving out oxygen 
when exposed to sunshine in larger ijuantities, as leaves do, they consume even 
more oxypn than before. Here we find the process which has brought the 
plant to this stage of growth is reversed, and in place of the decomposition 
which IS effected iiy light and actinism, we have a process of rcoxidation or of 
a close assimilation of eleinentH, precisely aiialogons to tliat which we detect 
upon the Daguerreotype plate and mi photographic papers under the iiilln- 
ence of the red rays. 
The results to which my experiments have led me, are— 
Isl. Light prevents the germitiation of seeds, 
ihd. Actinism quickens germination. 
pia^^t^' effect the decomposition of carbonic acid by tho growing 
4'th. Actinism and light are essential to the formation of the colouring 
matter of leaves. 
5th. Light and actinism, independent of the calorific rays, prevent the 
deve opment of the reproductive organs of plants, 
otli. The heat radiations corresponding with the extreme rod rays of the 
flowering of plants and the perfecting of their repro- 
I have been led to detect some very remarkable difFereoccs in the compo- 
sition of the solar rays by frequently examining the condition of the solar 
radiations, according to the plan described at the commencement of this 
lieport,^ for the pui'pose of ascertaining as nearly as possible tlie exact eon- 
itioijs in which the luminous, aclioic, and calorific principles exist. During 
the year 1816 and the commuuceraent of 1847, being engaged in selecting a 
g ass for the glazing of the great Palm House in the Royal Botanic Gardens 
