18—1845.] 
THE GARDENERS' 
CHRONICLE. 285 
“Tt is considered that this disease has been intro- 
‘duced since the hurricane, from some of the neighbour- 
ing islands, when it became necessary to replace a 
number of Cocoa-nut trees which had been destroyed ; 
but some pretend that it has been occasioned by the 
introduction of guano. Smoking, &c., has been of no 
avail, and as the insect most sagaciously places itself 
under the leaflet, where it is protected against the 
weather, the heaviest rain does not affect it, It has 
been advised to root up all Cocoa-nut trees in the 
island, and after the lapse of a year, when it is thought 
the insect may be destroyed, to replant the plantations 
from seeds imported from an island where the insect 
does not exist.", 
On earefully examining the leaves of the Cocoa-nut, 
36 is evident there are two distinct insects upon the 
under surface, an Aleyrodes and a Coccus. They ad- 
‘here to the under side of the leaf, and are surrounded 
by a whitish eottony or resinous powder ; both sexes of 
the Aleyrodes at rest and with their wings closed are 
exhibited, of their natural size, on a portion of the leaf 
(fig. 1), and also some oval animals producing the white 
powder in abundance from the margins of their sides, 
and these I suppose are the larva state of the Aleyrodes. 
There are also numbers of white linear cases, as shown 
at fig. 5, ‘which I conceive to be the pups of a male 
Coccus ; indeed I found one of the perfect insects stick- 
ing to the surface. At fig. 2 I have rep d th 
rangements? ‘To the first I answer I think it is likely 
to be the case from the concurrence of two causes. In 
the Polmaise method the heat of the fire is communi- 
cated to the plates of the stove, and thence appropriated 
by the passing current of air. Now, the property of air 
to appropriate, take up or absorb heat, is inferior to 
that of water ; as is evident from the circumstance that 
the plates of a stove may become red hot while sur- 
rounded with air, which could not happen if they were 
surrounded with water. The interior of the stove must 
be affected by this circumstance as well as the exterior 
—in other words, the interior of the stove will beraised 
to a higher temperature than the interior of a furnace 
surrounded with water, and the gases of combustion, by 
which so much heat is conveyed away into the chimney 
and lost, will partake of the same condition. This may 
be one cause of greater loss or waste of heat from an 
air stove than from a boiler or hot-water furnace ; and 
in the Polmaise method it concurs with another, arising 
from the circumstance of the fire being fed from the air 
of the house, which has already been warmed. ‘This 
is partly essential to the success of the Polmaise system; 
both the vivacity of the current and the renewal of the 
air of the house depend on the draught through the 
stove. But, in accomplishing these objects, what hap- 
pens? The abstraction of a portion of the air, to feed 
the fire, causes a partial vacuum within the house, and 
under side of one of the larvae; it is oval, concave, 
ochreous, and shining, with six minute legs and ventral 
rings, like a female Coccus ; but I could not detect any 
proboscis or antennze. I must, however, observe that 
* the objects had all suffered from extreme pressure and 
great heat, and it is not unusual for the proboscis to be 
broken off in removing such animals from the surface 
on which they are feeding, 
The winged specimensare larger thanany of our British 
Aleyrodes,* and from the neuration of the wings being 
different, as well as from tke remarkable anal forceps of 
the male, this insect might with great propriety be 
Separated from the genus Aleyrodes. A. Cocois is bright 
echreous, the head is rounded, the eyes are black, oval, 
and notched on the inside, and I think I could discern 
two minute ocelli on the inner margins ; the antennze 
are as long as the thorax, slender, and apparently seven 
jointed, basal joint stoutish ; second the longes:. The 
rostrum is stout and moderately long ; the thorax is 
nearly orbicular, the scutel distinct, the abdomen short 
and oval in the male, with the last segment long, nar- 
rowed, and cylindrical, producing two long ineurved 
claws, forming a pair of forceps (fig. 3); wings apparently 
horizontal in repose, clothed with white scales 
or irs, giving them a powdered appearance ; 
Superior ample, sub-elliptical, with a strong 
Costal nervure, and a fureate’ one with a longi- 
tudinal nervure beneath jt, issuing from near the 
"ase; inferior wings; smaller, with a single forked 
nervure, Six legs slender, hinder long but simple ; the 
‘tarsi biarticulate, basal joint the longest, the second ter- 
‘minated by two slender claws. Female similar, but the 
abdomen is ovate-eonie, the apex terminated by a very 
acute transparent valve with a small oval hairy lobe on 
each side (fig. 4). 
As insects will remain in an embryo state for long 
iperiods, every vestige of the infested trees should be 
burnt as soon as they are taken down, and the most 
diligent search must be made after the Aleyrodes upon 
Plants of the same naturalorder as the Cocoa-nut, to 
Ascertain if there are not colonies established elsewhere. 
There is the larva of a little beetle called Scymnus, 
which destroys the European Aleyrodes, and it is re- 
markable that no parasitic insect should have appeared 
to check the inerease of the Cocoa-nut species, but this 
may arise from the disease having been imported with- 
Out its usual attendant antidote. Fumigating with sul- 
phur wouid arrest the plague, if it could be applied ; 
but then it ought to be done simultaneously to be 
‘effective, or else at a season when the insects are in- 
Active,—Ruricola. 
ome Correspondence. 
Polmaise Heating.—The objections advanced against 
the Polmaise method of heating, as can make 
out, merge in a general charge of inefficiency and in- 
fompatibility with ical results on a large scale: 
To put it in a more specific form, it comes to this—that, 
With a given amount of fuel, equally well consumed, the 
Same temperature cannot be maintained in a hothouse 
by the Polmaise method, as by the hot water system. 
The objection, therefore, supposes a greater waste or 
loss of useful heat by the former than by the latter mode 
of warming. The questions then arise—first, Is it so? 
Second, 1f 80, is it unavoidable and inseparable from the 
System, or merely the incidental result of defective ar- 
= Gurtis’s Guide Genus, 436, 
a corresp g pressure of the cold external air, which 
Seeks to enter (and does enter by the laps of the glass 
and the chinks and crevices of the sashes and door 
frames), to fill up the void, and restore the equilibrium 
within and without. This in-draught of cold air, mixing 
with the warmed current, does doubtedly help to 
will provide for an inflow of air, amply sufficient to 
make good the consumption by the fire and draft of the 
stove, there cannot be any partial vacuum in the inte- 
rior of the house to cause a demand on the external air 
through the erevices of the glass and door or sash frames. 
The principle of this arrangement was developed in an 
ingenious plan by one of your correspondents under the 
signature “ Lusor,” in a late Number of the Chronicle, 
the only fault of which appeared to me to be that it did 
not carry it out sufficiently. In the annexed drawings 
I have endeavoured to extend it in conformity with 
the preceding observations. W is the outside of the 
back wall of the house,S the stove, and F F iron flue 
of the same carried horizontally to the end of the house, 
and then rising vertically above the wall of the house. 
C, a close chamber and air shaft or tunnel, sur- 
rounding the stove and flue, having openings to the ex- 
ternal air just below the coping, at the top of the flue 
or chimney ; these openings should be under regula- 
tion, and capable of being partially or wholly closed at 
pleasure. ‘he underground drain or pipe coming from 
the front of the house is double, or divided into two, D D, 
(see plan Fig. 2) one D opening into the ash pan P, 
which is otherwise quite close, and the other D com- 
municates with an angular chamber occupying the end 
of the stove, which opens into the chamber C, and may 
be fitted with a regulator or register plate, as is also 
the mouth of D, which opens into the ash pan. These 
divide the current from the under-drain into two parts, 
one going to feed the fire, and the other returning to 
the stove to be warmed, and enter the house again, for 
in the Polmaise principle the current has these distinct 
destinati th 
D 
reduce its temperature, and impair the efficiency of the 
system. The warmestadvoeates of the Polmaise method 
must, I think, admit that these disadvantages are fairly 
to be deduced from its operation as hitherto exhibited ; 
t which goes to the fire involving a 
renewal of fresh air from without, the other forming 
merely a part of the circulation, arising from difference 
of temperature between the stove chamber and the body 
of the house, which may still exist, but not in the 
same intensity and strength, though there were no 
and the second question then oecurs—are they unavoid- 
able and inseparable from the system, or merely the 
incidental result of defective arrangements? I own I 
should be less hopeful of its eventual success, and 
coming into general favour, notwithstanding the acknow- 
ledged benefit arising from the circulation of fresh air, 
which it provides for, if I thought that these objections 
(affecting its claims as an economical and efficient mode 
of warming) were incapable of being practically met 
and removed. But this is not the case; there are 
means for insuring an effectual appropriation of the 
heat evolved in combustion, in combination with an 
ample supply of fresh air ; so that there shall be no in- 
draught of cold air through the laps of the glass and 
other crevices. When the body of the stove is alone 
exposed to the action or contact of the passing current 
of air, the latter being unable to appropriate the heat 
as fast as it is evolved, a great portion will necessarily 
be conveyed away into the atmosphere along with the 
s of combustion, or be employed in heating the 
ior of the chimney 5 whieh, so far as useful effect is 
concerned, is equally wasted or lost. But let another 
arrangement be adopted, and the chimney (in its ordi- 
nary acceptation) be done away with ; and let the os 
ing apparatus consist of a stove, and a long EDU 
thin iron flue, entirely insulated in an UNO 
whieh the air, to be warmed and conveyed into the 
house, has to traverse. Under these circumstances, 
the heat diffused through the stove and flue, and 
radiated to the sides of tho tunnel, cannot fail 
to be appropriated and turned to useful account 
by the air in its protracted passage to the house, 
What is defective in the capacity of air for heat 
is compensated by the greater extent of heated 
surface which it is made to traverse, and consequently 
also by the greater length of time its particles are mov- 
ing in contact with it, And as the same arrangement 
with the fire and flue of the stove, and 
does not involve a renewal of the air. By means of 
the regulators at the mouth of the drain D, and at the 
top of the air-shaft, the current may be controlled 
at pleasure; when they are open the circulation will be 
rapid, the draft through the stove strong, and the fire 
brisk ; by partially closing them, these conditions will 
be moderated ; and when entirely closed, though the 
fire will be extinguished irculation of the at- 
mosphere of the house will still be maintained as long 
as any heat remains in the stove. The efficiency and 
economy of this arrangement admit of an easy test from. 
the temperature of the gases escaping at the top of the 
flue, which cannot be applied where an ordinary brick 
chimney is used. For in the latter case the tem- 
perature of the escaping gases is not a correct test of 
the loss of heat, as a great portion is absorbed in the 
masonry, which remains unaccounted for. But itis a 
correct test in the present case ; for whatever heat is 
taken up by the iron flue is either directly appropriated 
by the passing current, or radiated to the sides of the 
tunnel, from whence it is equally appropriated and con- 
veyed into the house. I wish to say a word about the 
stove, which, if coal is used, should be of the smoke- 
consuming kind, as Witty’s (represented in the drawing), 
which acts by distilling and coking the coal, and in- 
flaming the evolved gas. There are three very good 
reasons for this recommendation :—1st. Economy, as 
the smoke and soot are merely so much unconsumed 
fuel ; 2d. Soot, being a very bad conductor of heat, ob- 
structs and deteriorates the conducting property of the 
iron flue ; 3d. Much trouble in cleaning out the flue is 
saved. To those who prefer water as a magazine for 
heat instead of depending on a stove, and do not mind 
the additional expense of construction, an efficient 
heating apparatus on the Polmaise principle may be 
obtained by adapting these arrangements to a hot-water 
apparatus as represented in fig. 3. The flue, air tunnel, 
and under-drain, remain as before. Instead of a stove, 
let B be the boiler and furnace ; b 4, branches from 
the boiler to two hot-water pipes, P, running the whole 
length of the house; C, the curtain or wet blanket, or, 
what would perhaps be better, a woollen netting, with 
small meshes, through which the warmed air could find 
its way into the house.—J. H., H— B—ch, April 17. 
A Robin’s Nest.—In the greenhouse of a neighbour- 
ing gentleman there is a fine Cineraria, which, in addi- 
tion to its own beauty, contains a robin’s nest ensconced 
among the leaves, and by this time she must be sitting 
upon a full complement of eggs.— 4. B., Leatherhead, 
April 20. 
Martynia fragrans.—At p. 256 it is stated that 
Martynia fragrans cannot be successfully grown except 
jna house kept both damp and warm. In contradiction 
to this, I beg to observe that I have seen a very fine 
specimen growing in the open air on the end of an old 
Cucumber ridge. As a proof that it did reach per- 
fection as far as Nature was concerned, it perfected 
large bunches or racemes of its quaint proboscis-like 
seed-vessels,— G. 
Broccoli.—In addition to the many kinds of Broccoli 
which, during the last few years, have been in general 
cultivation, some other varieties have been raised, pos- 
sessing properties which their predecessors have not ; 
and being especially worthy of cultivation, as they pro- 
duce “ heads ” at a time when, under ordinary circum- 
stances, there is usually a succession most required. 
The Walcheren Broccoli, or Cauliflower, may be men- 
tioned as one of the most useful in this respect. In 
order to have a good succession from August to Jan- 
uary, I recommend sowing not earlier than the middle 
of April ; afterwards, a small sowing about every three 
