INFLUENCE OF SOLAR RAYS ON THE eROWTH OP PLANTS. 2? 
the yellow ray, but was produced by the orange, green and blue rays, and, 
as I infer, by the mean red. These esporiraents were made with great care, 
and the arrangement's of the beliostat, prism and lens appear to have been 
as complete as posfiiJ)le. I must, however, be allowed to express a doubt if 
the rays could bo kept stationary upou any line for so long a period as six 
and a half hours, and tlio slightest muvemeut would vitiate the e xperiment 
aud render it hazardous to declare that« the centre of the yellow ray is tho 
point of maximum etfi'ct in the production of cbloropliyl,'' 
My experiments, made in the same manner as Dr. (iardner’s, do not givo 
the same results. The method in which 1 pruccedeil was as follows:_A 
bchostat placed outside a window dirt'clcd a pencil of light upon a flint-glas* 
equilateral prism, and the prismatic sjicclrum was received io the dark cham¬ 
ber of an ordinary photographic camera; the place of the lens being occu¬ 
pied by a diaphgram which adcuitled the passage of Ujp spectral image only. 
My apparatus would not allow of ray keeping the sjjectrum upon the saino 
lines tor more than three hours, eveo when in the best adjuslmeiit. I found 
tJjat over every jmrt ot the spectrum giving light and colour recognizable by 
tlie unaided eye, tiie leaves of itetdlings of tlio coiiimon cress, mustoii 
tnigmonette and peas, which were in an etiolated state, became, after a longer 
or shorter tune, green. In those, as in the experiments previously named, 1 
louiid that every variety of jilant employed appeared to be inliuenced by dif- 
erent rays. Cress aud niustaid hecame grcmi the most rapidly in the green 
ray, migmonette in the yellow, and peas in the bine. It must be however 
observed that the influence was always uinst decided between the limits of tho 
mean orange and the mean blue my. mid that it took much longer to green 
plants in tlio red Hum it did in iho blue ray. 
Such are the results I have obtained with the sjjcctrmo ;and uolwitlistand- 
mg that objecrious have been urged against tlio use of coloured meilia in 
c^penraeiJts of this class, 1 am, after many years’ experience, convinced that 
there is no other way of obtaining correct results. All tho coloura of the 
s^petUrmn are merely modilicotions of the intensity of luminous power, and it 
AS been sliowii that light, heat and clicwical action, or aetinijini, arc common 
0 every raj', tlie difference being only jiroportional. TJierefore, iK'cause an 
CTcct IS produced in the yellow ray, we have no evidence that light alone is 
he agent; it may be due to the combined influence of light and the other 
principles. We have the means of analysing with great correctness the per¬ 
meability of coloured media, anil we can with considerable facility, by in¬ 
creasing the colour ov thickness of a fluid medium, produce almost any order 
n laUiation, which may be maiulained for days or months hi a emwtant cha¬ 
racter. A yellow modi.ini doc.« not inqily the use of a yellow light, or a red 
one the passage of red rays only; btii a well-regulated ycUow medium 
wi I give the most light with the lea-'t quantity of actinism, and a. blue one 
0 largest amount m actinism with the least quantity uf light. It will now 
understood that 1 place more coufideiico in the. results ubiaim-il under 
coloured media than any which oau be obtained with the prismatic spectrum 
upon growing plants. 
*'■ have seen that light is required for the secretion of carbon and the 
iberation of oxygen: we kno« that tlifi green colour of plants depends upon 
solar agency; but iiuh-sa we cun suppose light to be at one and the same time 
decornpusing carbonic acid and composing carbon, oxygen aud hydrogen in 
wie torni ol the waxy matter chlorophyl, which is not accurdiug to the usual 
^ ^1 pha?miinciui, we must look for information beyond that 
allorded us by the experiments iiotnetl. Indeed, under a solution uf bichro¬ 
mate of potash, and under a full yellow glass, I have had plants growing, 
