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needs in this respect are even more urgent no^Y than the}^ 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 l^e 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 Geographic Botanique Raisonnee. 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 tem])erature, either fixed or varied, mean or extreme, or the effect 

 of light, it is exceedingly difficult, and sometimes impossible (when 

 ol)-ervations 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 noAv 

 of a manufacturer, noAv 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 liuilt, 

 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 Avas but an accessory. I renew it now in the pres- 

 ence of an assembly admirably qualified to solve it. I should like, 

 were 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 Avould 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 

 two very transparent glass windows, hermetically fixed. Besides 

 which, there should be on the outside means of excluding the light, 



