188 INTERNATIONAL BOTANICAL CONGRESS. 
south, the other to 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, in order 
to obtain complete darkness, and to diminish the influence of the varia- 
tions of temperature when light was not required. By sinking it in 
the ground, by the thickness of its walls, and by the covering of its ex- 
terior surfaces with straw, mats, etc., the same fixed degree of tempera- 
ture could be obtained as in a cellar. The vaulted building should 
have an underground communication with a chamber containing the 
heating and the electrical apparatus. The entrance into the experi- 
mental 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 ne- 
cessary. 
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 germi- 
nation to flowering, and from this on to the ripening of the seed. For 
different species various curves could be constructed to express the 
action of heat on each function, and of which there are already some 
in illustration of the most simple phenomena, such as germination, t 
the growth of stems, and the course of the sap in the interior of cer- 
tain cells. We should be able to fix a great number of those minima 
and maxima of temperature which limit physiological phenomena. In- 
* See the electric apparatus of M. crees Seng ted at — in 
1857, denen i in the * Flore fae Barre et Jardins,’ vol. xii. Miscell. p 
termination s differe E degrees of conata bist, by Alph. Can- 
dolle, in - E omic héque ndis elle de Genève * (Archives des ciento) 
curves have not been constructed, ud data for their construction 
are, at least, dispersed throughout our books. I will cite, for instance, the 
que a a scape of Dasylirion, as observed by M. Ed. Morren (Belgique 
Lortic. 1865, p. 322). The figures there given are not favourable to the ac 
ed notion, that the growth of tissues is more active by night than by day. 
