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needs in this respect are even more urgent now than they were thirty 
years ago, and I can not do better than to reprint and indorse the 
following appeal first made in an address by A. de Candolle in 1866: 
It appears to me, however, that botanic gardens can be made still 
more useful in carrying out physiological researches. For instance, 
there is much yet to be learned on the mode of action of heat, light, 
and electricity upon vegetation. I pointed out many of these defi- 
ciencies in 1855 in my Géographie Botanique Raisonnée. Ten years 
later Prof. Julius Sachs, in his recently published and valuable work 
on Physiological Botany, remarks much the same deficiencies, not- 
withstanding that some progress has been made in these matters. 
The evil consists in this, that when it is desired to observe the action 
of temperature, either fixed or varied, mean or extreme, or the effect 
of light, it is exceedingly difficult, and sometimes impossible (when 
observations are made in the usual manner), to eliminate the effects 
of the constant variations of heat and light. In the laboratory it is 
possible to operate under more exactly defined conditions, but they 
are rarely sufficiently persistent; and the observer is led into error by 
growing plants in too contracted a space, either in tubes or bell 
glasses. This last objection is apparent when it is wished to ascertain 
the influence of the gases diffused in the atmosphere around plants, 
or that of the plants themselves upon the atmosphere. 
Place plants under a receiver, and they are no longer in a natural 
condition; leave them in the open air, and the winds and currents, 
produced at each moment of the day by the temperature, disperse 
the gaseous bodies in the atmosphere. Everyone is aware of the 
numerous discussions concerning the more or less pernicious influence 
of the gases given off by from certain manufactories. The ruin now 
of a manufacturer, now of a horticulturist, may result from the 
declaration of an expert; hence, it is incumbent on scientific men not 
to pronounce on these delicate questions without substantial proof. 
With a view to these researches, of which I merely point out the 
general nature, but which are immensely varied in details, I lately 
put this question: “ Could not experimental greenhouses be built, 
in which the temperature might be regulated for a prolonged time, 
and be either fixed, constant, or variable, according to the wish of the 
observer?” My question passed unnoticed in a voluminous work 
where, in truth, it was but an accessory. I renew it now in the pres- 
ence of an assembly admirably qualified to solve it. I should like, 
vere it possible, to have a greenhouse placed in some large horticul- 
tural establishment or botanic garden, under the direction of some 
ingenious and accurate physiologist and adapted to experiments on 
vegetable physiology; and this is, within a little, my idea of such a 
construction : 
The building should be sheltered from all external variations of 
temperature, to effect which I imagine it should be in a great meas- 
ure below the level of the ground. I would have it built of thick 
brickwork, in the form of a vault. The upper convexity, which would 
rise above the ground, should have two openings—one exposed to the 
south, the other to the north—in order to receive the direct rays of 
the sun, or diffused light. These apertures should each be closed by 
{wo very transparent glass windows, hermetically fixed. Besides 
which, there should be on the outside means of excluding the light, 
