162 
DR. DAURENY ON THE ACTION OF LIGHT UPON PLANTS, 
The next day, the thermometer being as on the preceding occasion, and the sun 
bright, sunflower A was placed under a frame glazed with orange-coloured glass the 
same as No. 5, and sunflower B under one glazed with blue glass as No. 2. 
In the evening it was found, that the tin vessel containing plant A had lost three 
ounces of water, and that containing B one ounce. Now in another experiment with the 
same plants, the tin containing A, placed under a frame glazed with blue glass No. 2, 
had lost six ounces ; that containing B, under one glazed with orange, No. 5, had 
lost 9§. So that although the ratio between the two was very different (being in the 
one case as 1 to 3, in the second as 1 to 1^), still in both there was a manifest su- 
periority in the orange over the blue glass with respect to its power of producing ab- 
sorption. Now orange-coloured glass seemed to act with about half the energy which 
belonged to transparent; for in another experiment upon the same plants, whilst the 
former had caused an absorption of four ounces, the latter had occasioned one of 
only two. 
'file same plants being next tried, one with a covering of transparent, the other 
with one of red glass, it was found that the former had absorbed 4^, the latter 2 
ounces, in equal times, the ratio being as 2'00 to '89. 
Hence the following may be stated as representing the relative amount of absorp- 
tion in these several cases : 
Under transparent . . 
Under orange .... 
Under blue, varying from 
Under red 
2-00 
1-00 
•89 
Similar experiments were tried with Vines, and with the Sagittaria sagittifolia, which 
latter being an aquatic plant, continued for a longer period in a healthy condition 
when immersed in the water. But in either instance the same exception was found 
with respect to the influence of light on the rate of absorption, as had been observed 
in that of exhalation, those glasses which radiated most heat, appearing to act upon 
the plant with an energy quite disproportionate to their illuminating power. 
'I’lie heat of the weather was very great during these experiments, the thermometer 
being frequently above 80°, and the liquor in the bottles often mounting as high as 
10.') , so that it would seem, that the heat radiated from the coloured liquid assisted 
in promoting absorption in the roots, as it appeared to have done in the former one 
in increasing the exhalation from the leaves. The same might have been the case, 
though in a lesser degree, when the blue or red glasses were the media employed, 
and thus certain irregularities observed in the results may perhaps be explained, by 
supposing that the joint action, of the light transmitted, and of the heat radiated from 
these screens, caused a greater exhalation from the leaves, and thereby produced a 
more abundant absorption by the roots to supply the deficiency. 
Upon the whole, then, I am inclined to infer, from the general tenor of the experi- 
