7:8 
THE TROPICAL AGRICULTURIST. [Aug. 1. 3902, 
other Botanical Gardens, were of immense benefit 
to the Empire. Moat people in this country knew 
£ew as a place where they could see beautiful and 
attractive things grow. It was, however, much more 
than that. The making the gardens attractive formed 
but a small part of the duty of Kew. It was a mighty 
organisation and the centre of the botanic activity 
of the Empire ; and Mr. Kidley would probably be the 
first to acknowledge the great assistance he had 
received in his botanical efforts from the Authorities 
of the Royal Botanic Gardens, Kew. — Imperial 
. Institute JowrnaU 
PHOSPHORIC ACID AND POTASH 
IN SOILS. 
The fertility of a soil is estimated, not by the 
total amount of chemical constituents which it 
contains, but chiefly by the availability of the plant- 
food ingredients. 
Phosphoric acid, though soluble in water, is not 
easily washed from the soil, either by rain falling 
upon it or by artificial waterings. 
In some recent investigations by Dr. Bernard Dyer 
with soils obtained from the Experimental Station at 
Bothamsted, it was found that there was little risk of 
loss of either phosphoric acid or potash, even if 
larger quantities are applied at one time than what 
are required for the immediate use of the growing 
crop, but that these elements accumulate in the upper 
layers of the soil, where they remain until taken up 
by the plant. It was, however, found that these in- 
gredients when derived from farmyard or stable- 
manure were less stationary than when derived from 
artificial manures; considerable quantities were found 
to have penetrated into the subsoil even as low as 27 
inohes from the surface. This is doubtless due to the 
more open and porous texture of the soil under the 
influence of continuous applications of large quantities 
of organic and bulky manures. 
When a manurial application of superphosphate, 
combined potash, and other mineral salts is made, a 
distinct influence is exterted in the retention by the 
soil of phosphoric acid in a less fixed and, therefore, 
presumably more available condition ; while if, for 
want of nitrogen in the soil, the growing plants have 
been unable to utilise all the phosphoric acid thus 
rendered available, more of it descends to the subsoil, 
as a result of the soluble action of these alkali salts. 
The importance has for many years been fully recog- 
nised by the intelligent horticulturist of applying nitro- 
genous manures in combination with phosphates, and 
the reason for this practice is shown in the foregoing 
statement. , , „ . , , 
In some of the vineyards of France it was found 
that there was a feeble development of wood, a falling- 
off of blossoms, diminished yield of Grapes, diseased 
leaves and roots, with a consequent retrogression of 
fruit quality. Attempts were made to remedy this 
defect by the application of abundant dressing of cow- 
manure— a material which has long been recognised 
to be one of tho best of fertilisers available for the pur- 
poses of viticulture ; nevertheless, this treatment 
proved utterly incapable of arresting the gradual ex- 
haustion of the soil. Old vineyards exhibit a conti- 
nuously progreisive fftlliog-ofi in fertility, and require 
digging at intervals, which become more frequent, 
or even, after a short period, they frequently hare to be 
replanted. It is readily conceivable that soil which is 
frequently being turned over, so that fresh portions are 
always brought in contact with the roots ramifying in 
it must, in courie of years, lose much of iti priitine 
richness, that cannot be completely restored by c«w- 
manure alone. 
The writer is acquainted with a plantation of Black 
Currant bushes which had been manured year after 
year with heavy dressings of peat-mosa manure, and 
yet this material utterly failed as a restorer of soil fer- 
tility; the Corraat-trees blighted, lost their leaves, and 
tbe fruit waa fcoaaty nnd of poor gnality. After 
various trials it was found that to ensure perfect nutri- 
ment of the bashes, and to render possible the pro- 
duction of good and full yields of fruit, chemical man- 
ures providing available phosphoric acid must be 
resorted to. Phosphoric acid is directly connected with 
the increased development of fibrous feeding roots 
within the surface soil, that enables the plant to obtain 
the maximum of benefit from raiofall and bright sun- 
shine. This is the special effect of phosphatic 
m?\nures when applied to superficially ro ted crops, 
such as Turnips, Onions, Potatos, Carrots, &c., and it 
is by virtue of this development that these crops eo 
markedly exhaust the available nitrogen within the 
soil, and especially of the surface soil. 
In regard to the element potash, it is sometimes 
stated that this ingredient is of relatively less import- 
ance than either nitrogen, phosphoric acid, or lime ; 
partly for the reason that lertile soils are naturally 
richer in potash, and because the generality of plants 
remove a smaller quantity of this element from the 
soils than of the other substances mentioned. 
Until recent years it had not been made quite clear 
what function potash exactly performed in the plant, 
although it has been proved over and over again that 
no plant is able to grow satisfactorily unless potash be 
present in a more or less available condition within 
the soil. 
A theory was at one time held that soda, which is 
not an indispensable plant ingredient, was capable of 
replacing potash in the plant ; but this has now been 
shown to be false- No other substance can replace 
potash, which is an essential constituent of all plants. 
According to investigations at Bothamsted, it is 
found that the presence of available potash in a soil 
is an important condition of the formation in plants 
of carbo-hydrates generally. It is always to be found 
in the actively growing parts of vegetation, as in the 
growing buds and shoots, and it exists in relatively 
large proportion in the seed. In the culture of Potatos 
potash is a most necessary ingredient in tbe produc- 
tion of the carbo-hydrate starch ; and in the culture 
of Turnips, Carrots, Beets, and all descriptions of frnits, 
the carbo-hydrate sugir is greatly dependent on a 
liberal available supply of potash — and the richer the 
soil may be in the element nitrogen, which necessarily 
increases the luxuriance and succulence of growing 
plants, the more potash will be required. In fact, 
the great function of potash is, that it acts as a carrier 
of the ingredient nitric acid to growing parts of vege- 
tation, and assists in the maturation, colouring, and 
ripening of fruits. 
Now, there are some Apples which are fit for table in 
early autumn, while there are others which only 
become ripe when kept over the winter. Experiments 
have shown that succulent fruits, such as Apples and 
Pears, are remarkably influenced by the diiSferent ele- 
ments of manure, not only with regard to their size, 
but also with regard to composition and maturity of 
the fruit juices ; thus, the substances, potash and phos- 
phoric acid, favour early maturity, while nitrogenous 
manures retard ripeness. Consequently, Apples and 
Pears that are required for early market or consump- 
tion, may be stimulated to forwardness by dressings 
of superphosphate of lime, basic slag, and potash ; 
while fruits that are grown more exclusively for winter 
use may be retarded by making the ingredient nitrogen 
of greater prominence in the manurial mixture than 
either potash, phosphoric acid, or lime. Further, the 
later crops having the whole season for their growth, 
greater dependence can be placed upon the natural 
resources of the soil.— J. J. Willis, Harpenden.— 
Gardeners' Chronicle. 
PLEOTRANTHUS AS A VEGETABLE. 
In a recent issue of the Journal de V Agriculture 
Tropicals, attention is called to a paper of M, 
Lemarie on the tubers of Plectranthus as a vegetable. 
These plants are Labiates, closely allied to the already 
known Stachys afSnis ; they produce tubers that can 
be need eimilarly, MM, Failiieux and Bois, who iq- 
