546 
JOURNAL OF HORTICULTURE AND COTTAGE GARDENER. 
[ December 14,1882. 
and becoming’ sou-. Charcoal and leaf soil not too much decayed 
are the best ingredients I have found for the purpose. All the plants 
should be well drained. With hardwooded plants it should be 
remembered when potting that they generally have to remain twelve 
or more months before being again repotted, consequently good 
drainage is of the first importance. Good peat, with a limited 
quantity of sand and firm potting, are the principal requirements of 
most plants of this class. The roots are small, and the plants gene- 
lally of a slow-growing nature, consequently their requirements are 
very different from those that are softvvooded and of much quicker 
growth. 
Much more might be said on potting. I have only made a few 
lemarks on it as far as regards the plants I have referred to. Young 
gardeners should watch the results of different methods of practice 
in the cultivation of useful plants, and be prepared in their turn to 
pursue, according to circumstances, that method which has proved to 
them the best. 
ODONTOGLOSSUM IIALLII. 
About three years ago I obtained a small pseudo-bulb of Odon- 
toglossum Ilallii, which has grown and flowered so well that I 
am induced to give some particulars of its size now and the treat¬ 
ment it has received, for it certainly is the most vigorous plant 
of the kind that has come under my notice. In the short time 
mentioned the small pseudo-bulb—about the size of a Broad 
Windsor Bean has increased to half a dozen, each from 3 to 4 or 
5 inches long, and from 2 to 3 inches broad. The spikes are 
being produced just now, and the foremost, which is hardly so 
vigorous as one or two which are only developing, is fully 5 feet 
long, and is showing twenty-seven blooms. The leaves are about 
a foot long, and the whole plant occupied a G-inch pot. These 
dimensions may, for aught I know, be far from uncommon, but 
are much above that of any plant I have hitherto seen, and I 
have seen many examples in the collections of even famous growers. 
Moreover, the pseudo-bulbs and spikes have increased yearly at 
an extraordinary rate, not merely in size but in numbers. In 
fact the number of breaks have doubled yearly, to say nothing of 
the increase of size. The hope, therefore, is not unfounded that 
by another season the pseudo-bulbs may be stronger and spikes 
more vigorous still. 
The treatment has been very simple. It has had a mixture of 
charcoal and fresh sphagnum, half and half, for a root medium, 
^ , j 13 k e pt confined at the roots, as I believe most Orchids 
should, for it seems that the soil does not become sour. So well 
have the roots liked this treatment that they have always been 
healthy and have filled the pots. The plant likes a constant 
moistness about the roots, at least when there is no sourness, 
even after the pseudo-bulbs have fully grown. If the flower- 
spikes come up the growth ceases ; but if these do not appear, no 
sooner is one set of growths made up than another set appears. 
When this happens to a Cattleya weaker growths are the result, 
but not in the case of the majority of Odontoglossums, which 
really do not want a resting season as long as they are not sub¬ 
jected to a too high and dry temperature. Advantage may be 
taken of this fact to increase the strength and bulk ©f such, for 
when kept growing by steady moisture and moderate shading for 
a season or two small healthy plants gain strength and size to a 
wonderful extent. When this object is gained it will be found 
that a little stinting for water just as the pseudo-bulbs near com¬ 
pletion, coupled with exposure to all the light possible short of 
scorching, will insure a free and a vigorous inflorescence. Though 
we ^ “little stinting,” it is not meant that water should be 
withheld so as to cause them to shrivel. This is often done to 
insure maturation and rest, but it only secures exhaustion. 
Can any of your readers tell me if my plant of 0. Halli has 
attained full strength ?—Single-handed. 
OF HUMUS. 
{Continuedfrom page 521.) 
I finished my last letter with an account of an interesting ex¬ 
periment by Ville which strikingly illustrated the solvent effect of 
humus upon carbonate of lime, and the consequent results on the 
yield of Wheat produced by its presence in conjunction with 
this mineral. Its effect upon the so-called insoluble phosphates 
through the carbonic acid which it generates was, it may be re¬ 
membered, fully shown in my letters on the value of phosphate of 
magnesia. In fact, there can be no doubt whatever that decaying 
organic remains in the ground do afford long-continued, if feeble 
sources of carbonic acid ; and wo can, when this truth is impressed 
upon our minds, better understand why it is that land exhausted 
y pmtivation should, when putrescible vegetable and animal re¬ 
mains are added to it, regain its fertility in a comparatively short 
time, and how it comes to' pass that the use of “ farmyard manure 
in the time of fallow will promote the process.” And here let me 
add a word from this point of view in favour of sewage manures, 
which from the most unbounded faith in their fertilising proper¬ 
ties have declined to so low a point that farmers can hardly be 
persuaded to cart them away when they can be had gratis. These 
manures are at all events characterised by a large proportion of 
highly putrescible organic matter, such as, in the case of earth- 
closet manure, appears, from the recent correspondence in your 
columns, to command the favour of horticulturists to an extent at 
least quite equal to anything I should contend for. To my mind 
it is clear that the chemist ought not to ignore in his returns the 
value of such organic matter, which at present he virtually does. 
To aid in bringing about a more reasonable mode of valuation is 
the object of these letters. 
The following table, extracted from the analyses of Boussin- 
gault and Lewy, of the air found in the interstices of different 
soils containing varying amounts of decaying vegetable matters, 
will assist us in a correct appreciation of the influence which 
humus confers by furnishing copious supplies of carbonic acid in 
the soil. The figures give the proportion of carbonic acid found 
in ten thousand parts of air, and it will be seen that the soil is in¬ 
comparably richer than the atmosphere in this active solvent, by 
which, as Liebig tells us, “the fixed elements of food are rendered 
soluble and capable of being distributed in all directions.” 
Indeed, having his mind directed very powerfully to the impor¬ 
tant influences of this gas, he goes so far as to say, “We know of 
no other way in which the earthy phosphates are dispersed 
through the soil than by means of carbonic acid and water,” 
which is, of course, saying more than he could with precision 
assert; but it shows the extent to which his mind was impressed 
by their action, and yet the substance which yields this solvent is 
not to be allowed a value in estimating the value of a manure ! 
But we will proceed with the promised table. 
Carbonic acid in 10,000 
parts of air by weight. 
Ordinary atmosphere. 6 
Air from sandy subsoil of forest . 38 
„ „ surface soil „ „ 130 
» ,, ,, „ „ vineyard. 146 
» i> ,, „ „ old Asparagus bed . 122 
»> >t ,, „ ,, ,, „ „ newly mnurd. 233 
ii ii „ „ „ pasture. 270 
ii ii ,i „ „ „ rich in humus . 543 
ii ii i, ,, „ sandy field (dry weather)) 
newly manured ) 
»> ii ii ii ,i i> ,, (wet weather)) 1413 
newly manured j 
It appears clear from the foregoing remarks that humus must 
assist materially in bringing into solution both phosphate of lime 
and carbonate of lime. But this is not all. The original sources 
of supply of the potash, soda, and silica found distributed in soils 
are the feldspaltic rocks. The soda and lime feldspars are often 
exceedingly durable. The decomposition of feldspar, when it 
does yield, consists in the breaking-up, through the action of the 
atmosphere, of the hardy glassy mineral into kaolinite (a hydrated 
silicate of alumina) and soluble substances which are removed by 
water. The hydrated silica when newly set free from combination 
is quite soluble in water, and together with the alkalies, when 
much water has access during the decomposition, is dissolved out. 
Thus 100 parts of potash feldspar, in being converted into kaoli¬ 
nite or pure clay, has removed from it 418 per cent, of silicic 
acid and 1G9 per cent, of potash. The high importance of car¬ 
bonic acid in a soil containing undecomposed silicates is therefore 
apparent, and the bearing of the table just given on this question 
can also be readily understood. S. Johnson, from whose work 
the figures given in the above table are extracted, after remarking 
upon the fact that the carbonic acid originates in large part by 
oxydation of organic matters, adds that this is strikingly demon¬ 
strated by the increase of its quantity resulting from the appli¬ 
cation of manure and the supervention of warm wet weather. 
“ It is obvious,” he says, “ that the carbonic acid contained in 
the air of the soil, being twenty to a hundred or more times more 
abundant, relatively, than in the common atmosphere, must act 
in a correspondingly more rapid and energetic manner in accom¬ 
plishing the solution and disintegration of mineral matters.” 
“ The vegetable and animal remains in a soil seem,” Liebig 
says in his “Natural Laws of Husbandry,” page 80, to “exercise a 
remarkable influence upon the diffusion of silicates. The expe¬ 
riments made on this point show that the absorptive powers of 
an arable soil for silicic acid is in an inverse ratio to the amount 
of organic remains in it; so that a soil rich in such remains will, 
when brought into contact with a solution of silicate of potash, 
have a certain amount of silicic acid unabsorbed, whereas an equal 
bulk of soil poor in organic remains will take up the whole of 
the silicic acid in the solution. The incorporation of decaying 
vegetable and animal matter will, therefore, in a soil containing 
