130 
THE FLORIST AND POMOLOGIST. 
perature, disperse the gaseous bodies in the 
atmosphere. Every one is aware of the nu¬ 
merous discussions concerning the more or 
less pernicious influence of the gases given 
off 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 with¬ 
out 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 tempera¬ 
ture might be regulated for a prolonged time, 
and be either fixed, constant or variable, ac¬ 
cording 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 presence of an assembly 
admirably qualified to solve it. I should like, 
were it possible, to have a greenhouse placed 
in some large horticultural establishment or 
botanic garden, under the direction of some 
ingenious and accurate physiologist, and 
adapted to experiments on vegetable phy¬ 
siology ; 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 
measure 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 two very 
transparent glass windows, hermetically fixed. 
Besides which, there should be, on the out¬ 
side, means of excluding the light, in order 
to obtain complete darkness, and to diminish 
the influence of the variations 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 exterior surfaces 
with straw, mats, &c., the same fixed degree 
of temperature could be obtained as in a 
cellar. The vaulted building should have an 
underground communication with a chamber 
containing the heating and the electrical ap¬ 
paratus. The entrance into the experimental 
hothouse should be through a passage closed 
by a series of successive doors. The tempera¬ 
ture should be regulated by metallic conduc¬ 
tors, 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, f Use 
* “ Geographie Botanique,” 1855, pages 49 and 
1346. 
+ See the electric apparatus of M. Carbonnier, ex- 
could be made of such an apparatus when 
necessary. 
Obviously, with a hothouse thus con¬ 
structed, the growth of plants could be 
followed from their germination to the ripen¬ 
ing 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 succes¬ 
sive phases from sowing to germination, from 
germination 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 illus¬ 
tration 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 he able to fix a great 
number of those minima and maxima of 
temperature which limit physiological phe¬ 
nomena. Indeed, a question more compli¬ 
cated might be investigated, towards the 
solution of which science has already made 
some advances—namely, that of the action of 
variable temperature; and it might be seen 
if, as appears to be the case, these tempera¬ 
tures are sometimes beneficial, at other times 
injurious, according to the species, the func¬ 
tion investigated, and the range of tempera¬ 
ture. The action of light on vegetation has 
given rise to the most ingenious experiments. 
Unfortunately, these experiments have some¬ 
times ended in contradictory and uncertain 
results. The best ascertained facts are, the 
importance of sunlight for the development 
of the green colouring matter, the decomposi¬ 
tion of carbonic acid gas by the foliage, and 
certain phenomena relating to the direction 
or position of stems and leaves. There re¬ 
mains 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 
Begions, produce in exhalation of oxygen, 
and in the fixing of green matter, as much 
effect as the light distributed from twelve to 
twelve hours, as at the Equator ? No one 
knows. In this case, as for temperature, 
curves should be constructed, showing the in¬ 
creasing or diminishing action of light on the 
performance of each function; and as the 
electric light resembles that of the sun, we 
hibited at Chiswick in 1857, figured in the “ Flore 
des Serres et Jardins,” vol. xii. Miscell. p. 184. 
* Germination under different degrees of constant 
heat, by Alph. de Candolle, in the “ Bibliotheque 
Universelle de Geneve” (Archives des Sciences], 
November, 1865. 
+ If the curves have not been constructed, the 
data for their construction are, at least, dispersed 
throughout our books. I will cite, for instance, the 
growth of a scape of Dasylirion, as observed by M. 
Ed. Morren (“ Belgique Horticole,” 1865, p. 822). The 
figures there given are not favourable to the accepted 
notion, that the growth of tissues is more active by 
night than by day. 
