746 THE TROPICAL 
AGRICULTURIST. [May i, 1888 
has laid down, that placing a certain value on the 
unit of nitrogen, the difference in the prices of the 
two manures was in just proportion to their intrinsic 
value, and offered rather warmly to produce Hughes 
fables of analyses in proof of his assertion. He 
further said that the difference in price between 
the two manures permitted of a proportionately 
larger quantity of cattle poonac being used. Now 
Hughes has said that taking 100 to represent the 
standard for purposes of comparison of white castor 
cake, coconut poonac, according to what was submitted 
to him for analysis, stood at 53, or a little more than 
half. "Will my friend, who uses 3 lb. of bones to 3 lb. 
of poonac for each coconut tree, therefore, if he uses 
castor cake, reduce the quantity of it to 1J lb. or one- 
half of the weight of bones? This is a proportion 
that no practical agriculturist will use, who has any 
regard for his trees. As to value, cocount poonac 
sells now at R45 the ton in the country. Is the 
price of castor cake twice asihigh ? 
M. Hughes has, in a letter to the Observer, dated 
lOthrJuly 1886, supplemented his aualysis of this most 
valuable cake, with an analysis of the inorganic matter 
or ash of the cake, as he says the previous 
analysis " does not afford information respecting 
the chemical composition of the mineral portion 
of the cake." In a note to his analysis he says 
that the cake has twice as much nitrogen as bone- 
dust, and five times as much as in 100 lb. of parch- 
ment coffee. Castor oake has 7*78 nitrogen as against 
2'80 in coconut poonac, and 2'68 of phosphoric acid as 
against l - 45 in poonac. The actual fertilizing matter 
removed from the soil by coconuts is what is repre- 
sented by the pooDac. For oil, which, when burnt 
leaves no residue, removes nothing from the soil. The 
branches, which, whenweaved, are used for estate build- 
ings, are again returned to the soil in their decomposi- 
tion, but unfortunately not to the exact spot on which 
they grew. The same with the husks, when not used 
for fibre. I am not aware whether an analysis has 
ever been made of the ashes of the husk, but they 
crystallize into a white salt which I believe is largely 
composed of potash, as shown by their cleansing power. 
But Mr. Hughes tells us that " castor cake yields an 
ash specially rich in phosphates of potash, , lime and soda, 
and these exist in a form readily available as plant 
food." From the above it will be readily seen that 
coconut poonac cannot be compared with castor 
cake as a fertilizer for coconut trees : indeed, consi- 
dering that it has more phosphoric acid than poonac, 
I think by its use we can dispense with the too stimu- 
lating bones'. Certainly not to be used in too large 
quantities, for even its great advocate, Mr. Lamont, 
says the quantity used is calculated by the ounce 
rather than by the lb. 
As to the wisdom of manuring trees not yet in 
bearing, every man is entitled to his opinion if it can 
be supported by science. Manuring, as I understand 
the term, is restoring to the soil the elements of ferti- 
lity removed by cropping : coconut trees not in bear- 
ing have removed nothing from the soil ; therefore 
manuring them is unnecessary, not to say positively 
harmful, especially with highly stimulating manures, 
which induce precocity in the first instance, 
and afterwards support a semi-artificial existence. 
Of course the practice has been suggested by so high 
an authority as Mr. Lamont, and it speaks volumes 
for him that he has found so ready an apostle in 
one, who, till very recently, held the opinion that 
manuring, or even disturbing the soil, was only to 
be resorted to when coconut trees showed signs of 
distress. As long as they bore well, it was not ne- 
cessary to nourish them at all. The transition from 
one extreme to the other is rather rapid. — Truly 
yours, B. 
INFLUENCE OF FRESH WATER ON PEARL 
OYSTERS. 
March 30th, 1888. 
Sir, — The great success that has attended the 
pearl fishery this seasoD will have made the panio 
at the prospeot of the first great loss almost a 
lorgotten incident of the past. I was one who, ha 
time permitted, intended to have advised the subse - 
quent seeking that took place, believing they would 
find. Your correspondent " Nemo," in your issue of 
the 27th, wakes an echo that deserves a word or 
two of comment, to prevent a miscarriage of opin- 
ion on the subject of which he treats in fashion 
somewhat ex cathedra. No oysters can live in 
fresh water only : that everybody knows, but all 
oysters that are so to speak ' gregarious ' of the 
' bed ' or ' bank 1 type, which the pearl oysters 
especially are, require for their food and sustenance 
the matters they assimilate brought down by the 
rivers discharging into the sea. In periods of 
drought these ' banks ' or beds of oysters will 
(by whatever process they are migratory) hug 
up to the river delta?, in search of food and modi- 
fied salt water. Hence your able Master Attendant, 
Capt. Donnan, reported millions of oysters on 
bank at known shoals before the floods, all vanished 
after, the oysters having beaten a retreat before 
the heavy floods. 
The principle of oyster growth and feeding has 
been etudied, and is well-known in America and 
elsewhere, where oyster cultivation has assumod 
enormous proportions. Patents for catching the 
' spat ' are simply legion in the United States. 
To give you an idea of the need of freshwater 
food and a modified salt water for the growth 
of the ' bank ' oyster, coast lands in the New 
England States are constantly advertized for the 
joint cultivation of cranberries (! ) and oysters — two 
orders of industry about as remote from each other 
as could reasonably be devised, one would naturally 
suppose ; but not so,— the cranberries require 
' bedwork ' irrigation, and a large supply of water 
approaching to swamp land, which after drainage 
is carried out to seaward over the artificial oyster 
bank for the sustenance of the oysters, which, as 
I said, require fresh as well as salt water for their 
healthy production. So that whenever you hear 
of oysters having vanished, the fresh flood has 
been too much for their digestion, and they have 
only moved away to a suitable position where the 
delicate admixture of salt and fresh water is more 
to their liking. Oyster dredging over the pearl 
banks has hitherto proved a failure, at least so it 
appears I am convinced the right sort of machinery 
has not been employed. I think that if a single 
chain ' clam shell ' with light ' tynes ' on it — 
were used, depth of water would be no difficulty, 
and the problem would be solved. I say a single 
chain "clamshell" simply because a double chain 
takes up so much more room on the ' drum ' where 
many fathoms have to be paid out. If this were 
to succeed, the Government haul would be three 
times as great as it is. Referring again to the 
' cranbery,' I see no reason why it should not 
form a valuable industry here; their production 
in the United States yields sometimes 50 to 100 per 
cent: what they most want is water. The berry could 
surely be acclimatized,* and they are very little more 
trouble than the cultivation of ordinary grass, if 
you only have the water. The demand for the 
"canned" cranberry being in excess of the supply 
by any conceivable quantity ; quite small farms 
yielding as much as £2,000 a year.— Yours, 
ENGINEER. 
[We have all along believed in the beneficial 
influence of the river water which enters the bay 
of Silavatturai, but we await Captain Donnan's deli- 
verance on the deleterious effect of floods. It seems 
possible that even floods of fresh water would do 
no harm were they unaccompanied by currents ? 
* That is the question ? Has it ever been known to 
grow in the tropics ?— Ed, 
