742 
THE TROPICAL AGRICULTURIST. 
[May 2, 1898. 
p. 362), and to German East Africa in 1894. But, 
as I stated in my letter of 16th December, 1896, it 
is not known to exist in the West Africa Colonies. 
Added to this, Liberian coffee is found to be only 
moderately affected by it. I cannot but think, there- 
fore, that all probability is opposed to the correct- 
ness of Sir Alfred Moloney’s statement that the 
disease existed in Liberia in 1875, as Eastern Africa 
was not affected till nearly ten years later. I should 
be glad to know on what precise evidence Sir Alfred 
Moloney bases it. If true, it seals the fate of coffee 
cultivation on the West Coast and seriously impe- 
rils that in the new world. 6. I enclose a memo- 
randum of the most approved method of treatment 
for dealing with scale insects. 7. A honorarium 
of one guinea (£1 Is.) is due to Mr. W. F. Bland- 
ford (whose address is 48, Wimpole Street, W.) for 
his assistance in the matter. — I am, etc., W. T. 
Thiselton Dyke. 
BIixtuhe foe Desteoyino Scale Insects. 
Heat milk nearly to boiling point and mix wi h 
double the quantity of kerosene ; stir briskly until 
a thick creamy liquid is obtained. Dilute with ten 
times the quantity of water. Spray or apply with 
a brush, keeping the mix.ure constantly stirred. 
Sour milk is as efficient as fresh. 
If milk cannot be obtained, or if the mixture is 
required in large quantity, a strong soap emulson 
may be used in its place. 
Copy op Minute by the Dieectoe of Gardens, 
SlKOAPOEE. 
Hor, Colonial Secretary. 
The scale insect is by no means rare here on Liberian 
coffee. It is usually a sign of weakness of the plant from 
want of nourishment. Liberian coffee is liable to a 
great many kinds of insect and fungus pests. — H. N. K, 
• — Selangor Government Gaxette. 
^ 
ANOTHER COFFEE PEST. 
I am afraid from what I see and hear, that a good 
deal of harm has been done to our coffee in more 
districts than one in a new way, The underside of 
the leaf becomes of a reddish tinge, it spreads rapidly, 
and soon affects the whole vitality of the coffee 
bush. I have pointed out to many fellow-planters, 
that where you have this, you have invariably a very 
small greenish white, louse-like insect. It has been 
maintained by some, that the injury must be caused 
b' a fungus, (it is certainly not the Hemileia vastatrix,) 
but I contend that the original damage is done by 
this insect. I have several times observed a rather 
larger, dark grey insect in the same leaves, and I 
w as almost sure from the first, that these were tlirips. 
They are a little different from any of which I have 
the description. But I am now satisfied that the little 
white lice are the larvae of thrips, and that this 
particular thrips has acquired such a liking for our 
crffee, that planters will have to light him seriously, 
lie can be killed by soap solutions, say one pound 
to 7 or 8 gallons ; but a better cure where tobacco 
is so cheap would be ; 
1 or 2 lbs. Tob-vcco. 
1 lb. soft soap, or common soap. 
20 gals, water. 
The soap should be cut into shavings and boiled, 
or dissolved in boiling water. The tobacco boiled 
separately and strained. 
Unfortunately the thrips prefer the underside of 
the leaves so that a syringe that would throw upwards 
in a fine spray is necessary. Better still, a spraying 
pump, such a.s is used in the American Orchards. This 
can be used to throw from the ground a fine mist-like 
spray that reaches practically every leaf. A brush 
might also be used to sprinkle these liquids. 
I Bend you a slide with these thrips mounted 
for the microscope. A couple of big, roundish insects 
are only aphides, which do no mischief to coffee, as 
far as I know. A mature thrips is on one side — the 
hairy wings mark it off from the others, and a number 
of the iarv® are also shown. There seem very few 
matuie thrips on the coffee at present. 
I trust that this notice may induce coreapondenoe 
the subject,— John W- Moir.— O eufrai African, Timet- 
NITRATES IN THE SOIL. 
A? soil fertility is of so much importance to horti- 
culturists, and as the productiveness of a soil is 
directly proportionate to the amount of nitrates 
which it contains, and the facilities or favourable 
conditions presented for the conversion of organic 
nitrogen into ammonia and nitrates, the subject of 
nitrification becomes one of intense interest to all 
cultivators of the soil. 
Nitre or saltpetre is a compound of nitrogen, which 
represents the form of combination in which nitrogen 
must be in order that plants may use it as food. 
The organic nitrogen of the soil, called its inhereut 
fertility, as w'ell as that contained in such fertilising 
matters as stable or yard-manure, dried blood, fish 
scraps, rape-cake, vegetable and animal-refuse, Ac., 
is not in a condition to serve as plant-food. To 
become available it must be converted first into 
ammonia and then into nitric acid. 
All nitrates are formed in the soil through the 
agency of small microbes or living organisms called 
bacteria, which require certain conditions for their 
proper growth and development. These requirements 
may thus be briefly stated : air or oxygen, a due 
amount of moisture, a proper temperature, that 
raiigii'g from 95° to 100° Fahr. being considered the 
best ; phosphates and other ash ingredients of plants, 
a mild alkali, such as carbonate of lime (chalk); 
and organic matter (humus) containing nitrogen. 
Shade is favourable to soil nitrification. The germs 
theniselves are in greater or less numbers in all 
cultivated soils, and in order for a soil to furnish 
the conditions necessary, as enumerated above, it 
must be loose and porous, so as to admit atmo- 
sp'neric air freely ; it must be well drained, and have 
good capillary action, so that at all seasons it will, as 
nearly as possible, contain that amount of moisture 
about it which is present when ground digs well, as 
this is found to be the degree of moisture most 
desirable. The soil should have p'enty of organic 
matter (humus) within it to furnish nitrogen, and 
favourably influence the supply of water. For this 
reason horticulturists find leaf-mould, pasture-turf 
soils, and peat soils so beneficial for plant-growing. 
Soils deficient in the nitric ferment germs or bacteria are 
barren, while those which furnish conditions favourable 
for nitrification, such as those enumerated above, are al- 
ways fertile. The total quantity of nitrates formed 
in a fertile soil is consMerable. Experiments have 
shown that they may range from 75 lb. per acre 
in an unmanured soil, to about 1251b. per acre in a 
soil to which farmyard manure has recently been 
applied. But it may be well to note that the whole of 
this nitrogen is not available to our ordinary cultivated 
crops, for the reason that many of them only assimilate 
the spring or early summer nitrates, the principal 
growth and power of assimilation haivng ceased by the 
month of J uly. Vegetable crops, such as Cabbage, Beet, 
Onions, Turnips, Carrots, Parsnips, Celery, &c., may 
still get hold of summer nitrates, but the nitrates 
produced in late autumn and winter are of little use, 
in so far as this applies to outdoor plants. The 
spring nitrification of a soil alone is, as a rule, quite 
insufficient for the requirement of early-spring plants, 
hence the advisability of using some stimulating 
manure, if very early production of vegetables is de- 
sired.— J.J. Willis, Harpenden.— GardcTters’ Chronicle- 
WATEEPEOoPiNfl Canvas.— The following are to be 
recommended :— (1) Good boiled oil coloured with a 
little lampblack or yellow ochre applied to the canvas 
when damp, and allowed to dry in a cool draught. 
(2) 1 gal. of boiled linseed oil, i lb. of common yellow 
soap, 6 lb. of yellow ochre, and 3 oz. of terebine. 
Dissolve the soap, cut in shreds, in about 1 qu. of 
boiling water, add the other ingredients, and boil 
together. Stir well to get thoroughly mixed while 
hot, and allow to cool before applying. Give two 
or three coats. (3) Litharge in the proportion of 1 
oz. to 1 gal. of linseed oil boiled together with some 
colouring pigment for twenty hours. (4j For purposes 
where cleanliness is no object, taipaulin canvas 
dressed with Stockholm tar is waterproof and pliable, 
but always luot'e ox less sticky,— Work, for April, 
