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in order to obtain complete darkness, and to diminish the influence 

 of the variations of temperature when lif^ht is not required. By 

 sinking it in the ground, by the thickness of its walls, and by the 

 covering of its exterior surfaces with straw, mats, etc., the same 

 fixed degree of temperature could be obtained as in a cellar. The 

 vaulted building should have an underground connnunication with 

 a chamber containing the heating and the electrical apparatus. The 

 entrance into the experimental hothouse should be through a passage 

 closed by a series of successive doors. The temperature should be 

 regulated by metallic conductors, heated or cooled at a distance. 

 Engineers have already devised means by which the temperature of 

 a room, acting on a valve, regulates the entry or exit of a certain 

 amount of air, so that the heat regulates itself. Use could be made of 

 such an apparatus when necessary. 



Obviously, with a hothouse thus constructed^ the growth of plants 

 could be followed from their germination to the ripening of their 

 seeds, under the influence of a temperature and an amount of light 

 perfectly definite in intensity. It could then be ascertained how heat 

 acts during the successive phases from sowing to germination, from 

 germination to flowering, and from this on to the ripening of the 

 seed. For dilferent species various curves could be constructed to 

 express the action of heat on each function, and of which there are 

 alread}' some in illustration of the most simple phenomena, such as 

 germination, the growth of stems, and the course of the sap in the 

 interior of certain cells. We should then be able to fix a great num- 

 ber of those minima and maxima of temperature wdiich limit phys- 

 iological phenomena. Indeed, a question more complicated might 

 be investigated, toward the solution of which science has already 

 made some advances, namely, that of the action of variable tempera- 

 tures; and it might be determined if, as appears to be the case, these 

 temperatures are sometimes beneficial, at other times injurious, ac- 

 cording to the species, the function investigated, and the range of 

 temperature. The action of light on vegetation has given rise to 

 the most ingenious experiments. Unfortunately these experiments 

 have sometimes ended in contradictory and uncertain results. The 

 best ascertained facts are the importance of sunlight for green col- 

 oring, the decomposition of carbonic-acid gas by the foliage, and 

 certain phenomena relating to the direction or position of stems and 

 leaves. There remains much yet to learn upon the effect of diffused 

 light, the combination of time and light, and the relative importance 

 of light and heat. Does a prolonged light of several days or weeks, 

 such as occurs in the polar regions, produce in exhalation of oxygen, 

 and in the fixing of green matter, as much effect as the light distrib- 

 uted during twelve-hour periods, as at the equator ? No one knows. 

 In this case, as for temperature, curves should be constructed, show^ing 

 the increasing or diminishing action of light on the performance of 

 each function; and as the electric light resembles that of the sun, 

 we could in our experimental hothouse submit vegetation to a con- 

 tinued light. 



A building such as I propose w^ould allow of light being passed 

 through colored glasses or colored solutions, and so prove the effect 

 of the different visible or invisible rays which enter into the compo- 

 sition of sunlight. For the sake of exactness nothing is superior to 

 the decomposition of the luminous rays by a prism, and the fixing the 



