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tive plants, those with colored foliage, as well as ordinary plants. 
The experiment might be prolonged as long as desirable, and prob- 
ably unlooked-for results would occur as to the form or color of the 
organs, particularly of the leaves. 
Permit me to recall on this subject an experiment made in 1853 by 
Professor von Martins. It will interest horticulturists, now that 
plants with colored foliage become more and more fashionable. 
Professor von Martins placed some plants of Amaranthus tricolor 
for two months under glasses of various colors. Under the yellow 
glass the varied tints of the leaves were all preserved. The red 
glass rather impeded the development of the leaves and produced at 
the base of the limb yellow instead of green; in the middle of the 
upper surface, yellow instead of reddish brown, and below, a red 
spot instead instead of purplish red. With the blue glasses, which 
allowed some green and yellow to pass, that which was red or yellow 
in the leaf had spread, so that there only remained a green border or 
edge. Under the nearly pure violet glasses the foliage became almost 
uniformly green. Thus, by means of colored glasses, provided they 
are not yellow, horticulturists may hope to obtain at least temporary 
effects as to the coloring of variegated foliage. 
The action of electricity on foliage is so doubtful, so difficult to 
experiment upon, that I dare hardly mention it; but it can easily be 
understood how a building constructed as proposed might facili- 
tate experiments on this subject. Respecting the action of plants on 
the surrounding air and the influence of a certain composition of the 
atmosphere upon vegetation, there would be by these means a large 
field open for experiments. Nothing would be easier than to create 
in the experimental hothouse an atmosphere charged with noxious 
gas and to ascertain the exact degree of its action by day and by 
night. An atmosphere of carbonic-acid gas might also be created, 
such as is supposed to have existed in the coal period. Then it would 
be seen to what extent our present vegetation would take an excess 
of carbon from the air, and if its general existence was inconven- 
ienced by it. Then it might be ascertained what tribes of plants 
could bear this condition and what other families could not have 
existed, supposing that the air had formerly had a very strong pro- 
portion of carbonic-acid gas. 
In hopes of realizing this idea of a complete botanic laboratory, the 
author spent his vacation of 1893 in the botanic gardens and green- 
houses of Harvard University. On his return to Washington Pro- 
fessor Riley kindly offered him every convenience and space in the 
insectary of the Department of Agriculture. His 300 experimental 
plants of wheat and maize were, therefore, brought hither from Cam- 
bridge, Mass. But unforeseen difficulties arose, and it is to be hoped 
that the idea of an experimental laboratory for botanic study may 
be carried out by abler hands. 
