250 
NEW AND RARE PLANTS. 
obtained from the combustion of plants of the same species which were to be cultivated. The pots in 
which the seeds were sown were enclosed in a large bell-glass ( cloche ) and hermetically closed. Every 
day the air of the interior was renewed by means of a large aspirator. But as this quantity of air, 
though considerable, could not contain enough of carbonic acid to supply the wants of the plants, an 
addition of five, then of seven per cent, of that gas was given by means of a preparation from which it 
was disengaged, bubble by bubble, as long as the renovation of the air was being effected. The air in 
being drawn from the bell-glass was made to pass into an analytic apparatus in which it was divested 
of the ammonia which it might contain. Thus two experiments were being made simultaneously: 
in the first [was ascertained], the dose of ammonia furnished with a certain quantity of pure air ; and, 
in the second, the ammonia of a nearly equal quantity of air, after that air had served for the nutrition 
of the plants enclosed in the interior of the bell-glass. 
In comparing the results of these two analyses, we perceive at once if the ammonia of the ah’ 
contributes to the development of the plants. On the other hand, we know by the analysis anteriorly 
made with a certain number of seeds of the species which have been operated on, the quantity of 
azote which was introduced into the bell-glass with the sowing. When the experiment is finished, we 
know, bv means of a similar analysis, the quantity of azote that the plants have assimilated during the 
course of the experiment, and, consequently, whether this azote comes from the ammonia or from the 
azote of the air. 
Although the plants have not yet been grown to maturity or gathered, we may consider this 
question as settled. It is indeed obvious that a certain quantity of azote has been assimilated by the 
plants, and that that azote comes from the azote of the ah: for the plants under the bell-glass have 
acquired a remarkable development, yet the ah, in being drawn from the glass, is found to contain the 
same quantity of ammonia as at the time at which it was enclosed. Moreover, it is possible the am¬ 
monia of the air might be assimilated totally by the plants: this conclusion is not altogether devoid 
of force, seeing that the ammonia that the ah introduced into the glass during four months that the 
experiments have been continued, hardly equals one or two centigrammes,* a quantity evidently too 
insignificant to produce any appreciable result in this phenomenon. 
Thus, the consequence alone deducible from the inspection of the glass was, that the azote of the 
ah was directly assimilated by the plants, and that the atmospheric ammonia had had no sensible 
agency. This result obtained, it remained for me, in order to complete the study of these phenomena, 
to determine the influence that a certain ouantitv of ammonia, added to the ah, exercised in its turn 
on vegetation. In order to enlighten myself on this new part of the subject, I again made a sowing of 
seeds of the same species as hi the preceding experiment. The pots were also placed hi glasses similar 
to the first, and the ah in the interior was then renewed 'with an aspirator of the same capacity. In 
the same way, also, an addition of five, then seven per cent, was made of carbonic acid. Indeed, all the 
conditions of the experiment were the same, except, however, a difference in the disengagement of a 
certain quantity of ammonia every day in the interior of the bell-glass. From the very first, the 
influence of this addition has been manifest. The leaves of the plants have assumed a beautiful and 
lively green: the stems have lengthened, and the branches, which have grown more n um erous, are 
full of leaves. But all the plants have not submitted, in the same degree, to the influence of the new 
agent: the cereals appear to be the most easily affected of all. In the glass in which the air is pure, 
the cereals are lanky and etiolated—their stems creep rather than shoot up. In the glass in which a 
portion of ammonia is added to the air, they are vigorous, straight, their stems erect, and even the 
leaves, which are numerous and abundant, take an upright direction. Thus a second conclusion is 
deducible from the single inspection of the apparatus: it is, that the ammonia which is added to the 
ah acts favourably on plants, and especially on cereals. 
Mm mb %m pirate. 
Pimelea macrocephala, Hooker. Large-headed Phnelea (Bot.. Mag., t, 4543).—Nat. Ord., Thymelaceae.— 
A fine greenhouse shrub, growing two to three inches high, with smooth erect, comparatively robust branches, 
furnished rather thickly with opposite, smooth, broad-lanceolate, thick, glaucous, stalkless leaves, which have the 
peculiarity, especially in the upper parts, of turning more or less in one direction—upwards ; the involucre consists 
of four to six leaves, larger and broader than those of the stem. The head of flowers is about two inches and a 
half across, the blossoms numerous, flesh colour, the tube slender and downy, with a limb of four spreading or 
recmwed segments, with ciliated margins. From the Swan Biver colony. Introduced by Mr. Drummond, about 
1848. Flowers in summer. Messrs. Lucombe, Pince, and Co., of Exeter. 
* A centigramme is equal to one-hundredth, part of a gramme, which is a little more than fifteen grains. 
