June 1, 1901.1 THE TROPICAL AGRICULTURIST. 
815 
THE PRODUCTION OF EXPORTABLE 
ORANGES. 
In a lecture on " Orange Culture and Diseases," 
delivered at a meeting; of the Malta Archeologioal and 
Scientific Society, Dr. J. Borg, M.A., M.D., made the 
following remarks concerning the production of 
oranges best adapted for export purposes :— 
" Too sandy and too compact soils are alike unsuit- 
able for the regular growth of the orange tree. This 
tree, when planted in a sandy soil, is very liable to 
suffer from diy weather. A sandy soil is, generally 
■peaking, a poor soil, because the nutritive compounds 
on which the tree subsists are very readily carried 
away by rain wuter, beyond the reach of the roots 
of the orange tree, which, it must be remembered, ia 
essentially a suvfafe feeder. A too compact soil keaps 
the water stagnant and is one of the chief causes of 
chlorosis. Moreover the roots are compelled to re- 
main very near the surface and therefore must be 
exposed to great heat in summer and to great cold 
in winter. Also, in a compact clayish soil the root 
iystem is particularly subject to dry rot. With 
regard to the chemical composition of the soil, we 
may say that the orange tree requires a soil contain- 
ing a high percentage of carbonate of lime and oxide 
ot iron, and only a moderate quantity of clay 
(alumina). When the percentoge of clay is very high, 
or when the orange tree is situated on a subsoil of 
clay, it produces fruit having a very thin rind, and 
a very luscious flavour, but, unfortunately, easily 
subject to rot and cannot be much depended upon 
for exportation. This is the case of some orange 
groves at the Boschetto. When the subsoil consists 
of soft porous rook, the fruit is large, has a thick 
rind, the oil glands and the aromatic properties are 
well developed. This may be observed in the orange 
groves of Casal Lia, Oasal Balzan, and Casal Attard, 
Malta- If the suosoil is, very hard and compact, 
and therefore very dry, as the subsoil of the orange 
groves at Musta, the fruit is small-sized, the rind 
is thin, but the pulp is very juicy and delicious. 
Fruit grown on such a subsoil ripens early and ia 
in every way suitable for exportation. Whatever 
the quality of the soil may be, still we may grow 
the orange tree to advantage, provided that the soil 
is so regulated that there will be a perfect drainage. 
A layer about two feet in thickness, and consisting 
of rubble and stones, and covered by two or three 
inches of thin rubbish will constitute by itself a 
perfect system of drainage to favour the flow of 
supsrfiuous water in winter. The layer of earth 
■which covers that of rubble should be t^wo feet in 
depth and never less than one foot and a half. Aa 
the rootlets will hardly ever penetrate beyond the 
layer of rubbish, and as drought prevents the for- 
mation of roots within six inches from the surface, 
we may say that the soil in which the orange tree 
thrives is from twelve to eighteen inches in thick- 
Bess." 
Concerning manures, Dr. Brog said :— " The orange 
tree does not exhaust the soil very rapidly. The 
produce of the orange tree are the fruit and the 
pruned branches, so that, strictly speaking, the soil 
is depauperated of its nutritive substances for the 
same amount which these substances enter into the 
tomposition of the fruit and the pruned branches. 
If the nutritive elements of the pruned branches 
are again returned to the soil in the form of wood 
ashes, we will find that, even after the lapse of 
several years, the orange grove can hardly be said 
to be impoverished at all. In the raising of crops of 
cereals and other annual vegetables we meet with 
the reverse. In these crops we carry off both the 
fruit and the plant which produced it, or in other 
•words the earth loses for ever all the nutritive 
substances absorbed by the action of tho roots. 
Now, the vast percentage of the weight of an orange 
consists of water and hydrocarbons, and of a few 
nitrogen compounds which the tree receives directly 
pr indire^^;^ {191:0 the 3,k, The small amoQUlj o{ 
phosphates and potash necessary for the formation 
of the fruit and the perfection of the orange pips 
is compensated by the stable manure which is sup- 
plied to the orange grove at regular intervals of 
six or eight years. The effect of a too liberal supply 
of stable manure on the orange grove is the produc- 
tion of exuberant foliage and large fruit with a thick 
peel. The fruit loses much of its aroma and becomes 
fibrous. On the contrary a soil very poor in nitrogen 
compounds produces tiny oranges delicious in flavour 
but unfit for commerce. The chemical manures 
which preferably should be supplied to the orange 
grove are the assimilable salts of phosphorous and 
potash. Already we see that the more experienced 
foreign cultivators are abandoning the use of nitrate 
of soda and have taken to use the superphosphates 
and " sulphate " of potassium in moderate quantities. 
To this chemical manure I prefer bone-dust and wood 
ashes, which are cheaper, less active, and have a 
more durable influence on the soil. Stable manure, 
particularly cow-manure, is an excellent compost for 
the orange grove, provided it ia sufficiently rotten 
to prevent any undue fermentation when supplied 
to the soil. But aa it contains a high percentage of 
nitrogen compounds, a liberal supply should be avoided 
to prevent the deterioration of the fruit." — Agricul- 
tural Gazette oj N. S. Wales. 
Gaseous Diffusion. — Dr. Horace Brown, F.R.S., 
in the course of a lecture of the Eoyal Institutionj 
said that : — 
" The question how the minute quantities of carbonic 
acid in the air found their way into the leaves in 
sufficient quantity to nourish the plant had long 
been a matter of controversy ; but it was now estab" 
lished that they entered wholly by way of the 
minute openings known aa stomates. But this fact 
presented a further difficulty, since the aggregate 
area of these stomates, when expanded to their 
fullest, was less than 1 per cent, of the total leaf* 
surface, and the amount of carbonic acid taken in 
by the leaf was such that it must enter by these 
openings more than fifty times faster than it would 
if each of them were filled with a constantly renewed 
solution of strong caustic alkali. There appeared to 
be only one way out of the difficulty, and that was 
the assumption that the leaf knew more about the 
laws of free diffusion than we did. This was proved 
to be the case. If diffusion of gas were established 
down a cylinder of equal diameter from one end 
to the other, the rate, other things being the same, 
varied directly as the area of the cross-section of 
the cylinder. But if the cylinder were obstructed 
somewhere in the line of flow by a thin diaphragm 
pierced with a single circular hole, the accelerntion 
of flow was inversely proportional to the diameters 
of the apertures — as the aperture was made smaller, 
the flow through a 'given unit of area was pro- 
portionately increased. Since the stomates corres- 
ponded to the latter case, it became easy to under- 
stand how, in spite of the small area of leaf they 
occupied, they could drink in the atmospheric 
carbonic acid with such rapidity ; the leaf consti- 
tuted a multiperforate septum, and the distance at 
which the stomates were arranged on the underside 
of most leaves was that which by experiment had 
been found the most economical arrangement of very 
small Rperturea in such a septum." — Times,—' 
Gardener's Chronicle. 
♦ 
THE CUTIVATION AND USE OF SUN. 
FLOWER SEED. 
The common sunflower, Helianthus annuus, is a 
native of Mexico and the northern portions of South 
America, and was probably first brought to Europe 
by the early Spanish expeditions to Peru and Santa 
Fe, since it was grown at Madrid in the sixteenth 
century. The plant has, therefore, long been known 
in most Knropean countries as an ornamental shrub, 
but in Russia it has for many years been extensively 
CHUmted 9s m. eeooomic product, la ii^dg, Mr, 
