5qo Influence of Heat and Light on Vegetation. [October, 
means of a petroleum lamp. Under similar bells of coloured 
glass, plants had been found capable of passing through 
their entire vital cycle without displaying any anomalous 
phenomena or yielding unusually small crops. 
To determine the influence of different colours of light 
two bells were selected, the one of blue and the other of 
yellow glass, both of a medium shade. 
The blue glass, coloured with cobalt, — as was found on 
examination of its spectrum,—- transmitted, in addition to 
the blue and violet rays, the red and the green, apparently 
unhindered, the orange and yellow only being extinguished. 
The yellow glass, coloured with carbon, tiansmitted all 
the rays except the blue and violet. The absolute intensity 
of the light was manifestly greater under the yellow bell 
than under the blue. 
The barley-plants under both bloomed normally, formed 
good, perfect ears, and ripened finally in the ordinary manner 
without being distinguishable from other plants placed for 
comparison under a colourless bell. 
The weight of all parts of the plants above the surface, 
when dried, was from the yellow bell 5291 m.grms., and 
from the blue bell 4431. . . 
Two new pots of equal size were then planted with 
sprouting barleycorns, and placed under coloured bells. The 
blue bell was of the same colour as in the former experiment, 
whilst the yellow bell was darker, and the absolute bright- 
ness under it was small. The violet ray was quite extin- 
guished, and the blue nearly so. Both plants showed nothing 
anomalous in their growth which might be asciibed to the 
specific adtion of the coloured light, ihey seemed meiely 
like plants which had been partially withdrawn horn the 
diredt sunshine. There was no diffeience between the two, 
save that the plant under the yellow bell, which was the 
darker of the two, was the earlier in showing signs of weak- 
ness. The plant from the yellow bell gave 2*5725 m.grms. 
of dry substance, and that from the blue bell 2*7990. 
It thus appears that plants are not very sensitive to mo- 
derate changes in the qualitative composition of the sunlight 
to which they are exposed. 
It need scarcely be added that the wonderful effedts which 
have been ascribed to the blue ray, or rather to light passing 
through ordinary cobalt-blue glass, cannot be considered as 
scientifically demonstrated. 
