232 
THE TROPICAL 
AGEICULTURIST. [Oct. 1, 1899. 
To generate the gas ' the required quantities cya- 
nide and water are first placed in the generating vessel, 
the cyanide being broken into small pieces about the 
size of lump sugar. The operator then adds the acid, 
pouring it slowly into the vessel to avoid splash- 
ing, and immediately withdraws.' 
The above treatment is suitable for fruit and hardy 
plants. Tender garden plants are usually imported 
in Wardian cases, and may be treated separately. 
We have— in the ' Wardian case' — an air-tight chamber 
ready to hand, in whicn the plants can be fumigated 
before their removal. After a large series of ex- 
periments with various fumigating media, I find that 
hydrocyanic acid gas remains by far the most effi- 
cient insecticide and the least injurious to the plants. 
But with delicate succulent plants I find it has to 
be applied rather difierently. A more concentmted 
dose of the gas applied for a shorter period is most 
satisfactory in its results. In a Wardian case, con- 
taining about sixteen cubic feet, I find a dose of i 
ounce cyanide, ounce acid, and 1 ounce water, with 
an exposure of half an hour, will kill every indivi- 
dual of a colony of Orthezia fthe most resister.t of 
all Coccidsj without in the least affecting the 
plants. The treatment should be carried out only 
after sunset. According to Mr. Lounsbury's tables, 
these proportions of chemicals should be sufficient 
for a space of 140 cubic feet with a longer exposure. 
The other meterials tested wered^ a preparation 
of concentrated nicotine, sold by the XL-all Com- 
pany; (2) McDougall's fumigation paper ; (3) 3 eyes' 
fluid; (i) naphthaline; and (b) common tobacco 
leaves, Nos. 1, 3, and 4 were evaporated by means 
of a small spirit lamp inside the case; Nos. 2 and 
were lighted and allowed to smoulder. All these 
materials, applied in different lengths of time, re- 
sulted similarly in more or less complete injury to 
the plants, and very incomplete destruction of the 
insects. 
If there be no Government quarantine establish- 
ment in the general planting interests, importers 
should safeguard themselves individually by properly 
disinfecting all foreign plants before distributing 
them or putting them out in their gardens. 
Further directions! or the application of the 'gas 
treatment ' will be found in the sections treating of 
CuBATiVE Measures. (Sec pp. xxvii — xxxi.) 
Perhaps of equal importance as a preventive 
measure is the maintenance of plants in a vigorous 
free-growing condition. This is a fact that has been 
recognised by gardeners for many generations. Any- 
thing that interferes with the free iiow of sap im- 
mediately lays a plant open to attack from its in- 
sect enemies, A weakly, hide-bound plant falls an 
easy prey to every pest. Scale insects in particuls.r, 
with a few exceptions ('and such exceptions chiefly 
imported series), seem to avoid a free-growing plant, 
possibly finding the healthy rush of sap too strong 
for them. Unremitting attention to cultivation will 
go far towards the prevention of insect pests. 
Amongst causes predisposing to disease may be 
mentioned: (1) Careless selection of plants and the 
retention of " weakly seedlings ; (2) Insufficient or 
injudicious drainage ; (3) Unsuitable condition of 
soil, want of tillage, and— perhaps— of fertilisers. 
Under the category of remedial measures may be 
mentioned the use of resistant stock. In the history 
of nearly every extentsive plant disease it has been 
observed that individual plants— or established vari- 
eties of the plant— may show a marked freedom 
from the disease prevalent upon the less favoured 
type, liy breeding from such individuals, or accidental 
varieties, a more or less completely resistant stock 
may be established. This fortunate fact has been 
frequently used with great success in dealing with 
fungal diseases. Thus a special variety of the potato 
plant— proof o,gainst the well-known potato disease- 
has been extensively cultivated. Some varieties of 
wheat are found to suffer but little from 'wheat 
rust' (Fuccinia). We have also examples of certain 
established strains of cultivated plants that repel 
particular insect pests. In Europe the vine growers 
bave fvun^ American (3l9cJi that io a Iwge ex- 
tent resists the attack of the dreaded PhyUoxera ; 
and by grafting on to this hardy stock they have 
been able to immunise their more delicate and valu- 
able varieties. In Ceylon we have the strocgest evi- 
dence that certain varieties of the tea plant Ces- 
pecially the Assam indigenous stocky are most 
markedly free from injury by the so-called 'mosquito 
blight ' (Helojidtis). In any serious epidemic that 
may threaten the profitable cultivation of an economic 
plant, we should at once be on the look-out for any 
accidental varieties or strains that may prove 
resistant to that particular disease. In cases 
where the hardier stock is not otherwise so profit- 
able as the more delicate variety, by grafting upon 
it a moi'e valuable scion the latter may sometimes 
be rendered equally immune. 
Curative Measures. 
Where preventive measures have failed, as — even 
with the greatest care — must often happen, recourse 
must be had to curative measures. 
In no single connection can the old proverb, 'A 
stitch in time saves nine,' be more aptly applied 
than in dealing with insect pests. In this case the 
'stitch in time' is more likely to save ninety, or 
nine hundred, or nine thousand ! 
If a pest is to be eradicated, mmetftafe treatment 
is the most important part of the process. 
And the first step towards treatment should, when 
possible, be the insolation of the infected area. All 
ordinary work amongst the affected trees should be 
deferred until after treatment. The yoijng larvae of 
scilc-iusects are very minute and active, and one of 
the most fertile sources of their distribution is by 
means of clothing. The rough 'cumblies' used by 
the estate coolies are particularly well adapted for 
their transport. . 
Another important point is that the treatment 
should be applied on the spot. If the infected blanches 
are cut down .and carried off to' some other part to 
be burned, they may be shedding the germs of the 
disease all along the way. 
It; is difficult to lay down hard-and-faet rules for 
action, so much depends upon circumstances, e g. the 
nature of the particular pest, its extent, the i,atnre 
and value of the plant attacked, &c., &c. But for, 
the sake of example, we will suppose a case in 
which three or four tea bushes are found to be in- 
fested by some scale-insect that is considered to be 
a dangerous pest. First dig a fair-sized hole in the 
midst of the affected clump, and place in it some 
dry grass and sticks as foundations for a fire. Pill 
two or three buckets with one of the insecticide 
washes described below. Prune back the branches 
one by one ; immerse each branch completely in the 
insecticide and throw it into the hole, until nothing 
but the bare framework of the tree is left. Sweep 
all fallen leaves and rubbish from beneath the trees 
into the hole. Next, paint over the bare stems with 
the same insecticide, using a large paint brush and 
taking great care to saturate the entire surface down 
to the ground. Then set fire to the heap of prun- 
ings, and cover up the remains with earth. To kill 
off possible stragglers, the unpruned trees immedi- 
ately surrounding the affected patch should be tho- 
roughly sprayed with the mixture. If carried out 
in time, these measures will probably stamp out 
the pest ; but a careful watch should be kept for 
any fresh outbreak. 
The above treatment is suitable only for such 
plants as may be cut down without permanent in- 
jury. We may now consider the case of some larger 
tree to which this method would be inapplicable — 
Bay an orange or cacao tree. In shis case the gas 
treatment is the most suitable. The application 
should be repeated after an interval of about a 
fortnight, to ensure the death of larvae subsequently 
hatched from eggs that may have survived the first 
operation. Full directions for gas treatment are given 
below. (See pp. xxvii — xxxi.) 
In other cases a combination of these two method 
might be adopted. If two or three coffee tree 
sh9ul^ reqtiir? treatment, aU superfluous branches 
