578 
August 2, I9i.^, 
THE GARDENERS’ MAGAZINE. 
contrast to the type. These eiistomas are 
best treated as biennials, and flowered the 
year after the seed is sown. 
Pavetta caffra. 
Each recurring summer this forms a 
pleasing feature in the cool portion of the 
T range, yet, for some reason or other, it is 
rarely, if ever, met with elsewhere. It 
forms a neat-growing, freely-branched 
shrub, clothed wdth smooth, obovate leaves, 
while the flowers, which are borne in great 
profusion in compact, rounded heads, are 
white with long prominent stamens, l^ing 
a native of Caffraria, this pavetta needs 
rather more heat than those from the more 
southern part of Africa. In the days of 
the old Chiswick shows this pavetta used 
to figure among the specimen plants then 
exhibited. 
Ddedalacanthus Watti. 
This is a near relative of the popular 
Dsedalacanthus nervosus, which is more 
generally knowm in gardens as Eranthemum 
pulchellum. From the older kind D. Watti 
differs from its being dwarfer in habit, 
while the flowers, which are about an inch 
across, are of a deep bluish-purple colour. 
It also flowers much earlier, as is well 
shown in the case of a group of plants in 
the intermediate portion of the T range. 
Where glass structures have to be kept gay 
at all seasons, both these species of Dsedala- 
canthus are exceedingly useful for the pur¬ 
pose. D. Watti is also known as D. parvus. 
Lindenia rivalis. 
This strange flower, somewhat like an ex¬ 
aggerated bouvardia, is in bloom in the 
stove portion of the T range. It forms an 
evergreen shrub, is a native of Mexico, and 
the white blossoms are borne in few-flowered 
corymbs. They are star-like, about IJ 
inches across, and with a corolla tube six 
inches long, the latter giving to plants in 
bloom a singular appearance. 
Costus speciosus. 
This member of the Ginger-wort family 
is common in India, but it is not often met 
with in cultivation here. From a stout root- 
stock are produced erect, leafy shoots to 
the height of a yard or more. They are 
terminated by a cone-like head of bracts, 
from whence the flowers are produced. In 
the case of C. speciosus they are of a 
satiny white tint, while in another species 
—C. igneus—which blooms later in the sea¬ 
son, they are of a brilliant orange hue. 
Costus speciosus is now in flower in the 
T range. 
Combretum purpureum. 
Though long in cultivation, and at one 
time far more generally met wdth than it 
is now, this combretum always arrests the 
attention of visitors to Kew when in flower. 
It is trained to the roof of the stove por¬ 
tion of the T range. The oblong, lanceolate 
leaves are of a dark, shining green, and the 
flowers are borne in panicles, and are of a 
pleasing shade of light scarlet. This com¬ 
bretum is also known as Poivrea coccinea ; 
indeed, this is the name under which it oc¬ 
curs in the Dictionary of Gardening,” but 
at Kew the older name of Combretum is 
retained. 
The Victoria. Lily House. 
The gigantic water lily, from whence this 
structure derives its name, is not yet in 
bloom, but in the same tank two of the 
blue-flowered tropical species of nymphsea 
are blooming freely. They are the Austra¬ 
lian Nymphsea gigantea and Nymphsea stel- 
lata, which is a native of tropical Africa 
and Asia, and of which several varieties 
are in cultivation. K 
PARTIAL STERILISATION OF 
SOILS 
Within a quite recent period we have re¬ 
ceived several inquiries about the most ad¬ 
vanced methods of partially sterilisation of 
soils used in crop production under glass for 
the purpose of suppressing insect and fungoid 
contained therein. The most recent in¬ 
formation available on this important sub¬ 
ject is that contained in a lengthy report 
by Dr. E. J. Russell and Mr. F. B. Peth- 
ridge which was published in the issue of 
the ” Journal of the Board of Agriculture ” 
for January last. Both Dr. Bussell and Mr. 
Pethridge have devoted much attention to 
the investigation of soil sterilisation, and 
the results of their researches cannot be too 
widely known. We publish the portion of 
the report relating to the methods of pro¬ 
cedure in the partial sterilisation of soil by 
heat and chemicals, and refer those of our 
readers to the issue of the publication con¬ 
taining the report for particulars of the re¬ 
sults obtained in dealing with the various 
crops included in the researches. 
Partial Sterilisation. 
There are two general methods of partial 
sterilisation. The soil may be heated to 
about 200 degrees F. by steam or dry heat, 
or it may be treated with chemical antisep¬ 
tics. Up to the present time heat has been 
found to give the better results, because it 
not only kills the various detrimental and 
disease organisms, but it also brings about 
a certain amount of decomposition, thus 
lightening the subsequent work of the food¬ 
making bacteria, while in some instances it 
improves the physical condition of the soil. 
Chemical treatment is cheaper and more 
convenient in practice, but, on the other 
hand, is less effective, even when thoroughly 
done; it is also difficult to effect thoroughly, 
since some of the antiseptics cannot readily 
be distributed uniformly in the soil, even 
by watering, because they are absorbed by 
the top layer of soil from their solutions or 
emulsions. 
None of these difficulties are insuperable, 
and it would be premature to offer any 
opinion as to which method will finally prove 
better for the grower. The more effective 
must in the end be the more profitable, but 
there is nothing to show that chemical treat¬ 
ment will always be less effective than heat, 
and, in fact, the difference between them has 
been distinctly reduced by the use of new 
antiseptics. 
Partial Sterilisation by Heat. 
Two methods of partial sterilisation by 
heat are in use. In one the soil is heated 
directly by means of a coke fire; in the 
other it is subjected to the action of steam. 
The choice is largely dictated by convenience 
and engineering detail, there being no suffi¬ 
cient evidence of any difference in effective¬ 
ness when the soil is equally heated in both 
cases. 
In the direct heat sterilisers the soil is 
heated for a number of hours, and is then 
removed to make way for another charge; 
the process is practically continuous, and 
can be worked with but little labour. There 
are several advantages in working with moist 
rather than dr;y soil; the danger of over¬ 
heating is minimised, and the heat travels 
more rapidly and uniformly throughout the 
mass, since moist soil is a better conductor 
than dry soil. 
Several methods have been adopted for 
heating by steam. Perhaps the best known 
consists in blowing steam into the soil 
through a gridiron-shaped instrument 4 or 
5ft. by 3 or 4ft., made in lin. pip¬ 
ing perforated with holes one-eighth of an 
inch in diameter. This instrument is placed 
in a wooden frame without top or bottom, 
and capable of holding a load or more of 
soil. Soil is then filled in, and the whole 
IS covered with sacks. Connection with the 
|x>iler is made by a 2in. hose pipe and steam 
m blown in for about 20 to 30 minutes. 
W hen high pressure (801b.) is available a 
larger amount of soil can be treated at once; 
when only low pressure can be used, the soil 
•should not he too wet to begin with, or u.ck 
condensation may occur. ConsiderabI, 
economy can 1^ effected by performing ,t 
operation in the house itself An3 
the tackle along the borders’as each^i^ 
IS treated.* 
Another implement used in precisely tb 
same manner is shaped like a harrow thi«^ 
also made of gas piping, but is fitted wb't 
nine or more tines of smaller piping 
forated with holes, out of which the sUan,' 
issues. 
An appliance adopted in America is ©r 
the principle of a warming-pan. A galvanised 
iron vessel, 10ft. by 6ft. by 6in. is connected 
with the boiler, and then passed down an 
inch or two into the soil which has alreadt 
been prepared for the plants. Steam is now 
blown into the vessel for 40 minutes at a 
pressure of 1001b.; none escaiies into the 
soil, but there is considerable passage of 
heat. The process is sometimes done bv 
contract, and is estimated to cost about a 
shilling for 33 sq. ft. We have not seen the 
process at work, and do not know that it ii 
in use in this country. 
In the gridiron or harrow method it is 
hardly necessary to use a thermometer; the 
temperature cannot rise above 212 degree: 
F., and will not usually be much below if 
the steam is at the pressures already men¬ 
tioned. The soil, after removal from the 
sterilising frame, may be thrown into a heap, 
and cools so slowly that the sterilising pro¬ 
cess still continues. The heap, however, 
should not remain out of doors for long 
without protection; every shower of rain 
washes away valuable plant food, and every 
wind may bring plant disease germs and 
other undesirable organisms to repopulate 
the soil. Among the advantages of sterilis¬ 
ing inside the house is the avoidance of tbe.M' 
sources of injury. We have not yet sufficient 
data to determine the cost, but we have ?*cen 
houses done at a cost of 4d. to 6d. per m|. 
yard. 
It is not yet possible to say whether soils 
may profitably be sterilised very long before 
they are wanted. In commercial cucumber 
houses, for example, there would be obvious 
advantages in carrying out the sterilisation 
during the slack months from October on¬ 
wards ; but as the borders are not made up 
till February, the risk of infection is 
creased if the treatment is carried out too 
early. In course of time a copious developj 
ment of mould often takes place in heated 
soils carrying no crops, but we have no evi¬ 
dence that it is detrimental to plant gro^fl- 
This, however, is essentially a matter where 
convenience counts; even if a loss does go 
in the stored soil, it may be advantageous to 
sterilise early when work is slack. 
Seeds sown during winter and early spriw 
in tbis heated soil do not 
quickly as in untreated soil, and ^ ^ 
lings are apt to be rather stunted and dar 
green in colour. Tomatoes also show a puHf 
colouration in the stems and the backs oi i 
leaves. Fig. 2 shows a box of 
seedlings in heated soil side by side ^tn 
other lot sown the same day in the sa 
soil, which, however, had not been 
Bad seed is more affected than g<^ ‘ _ 
Young plants raised in heated soil alw 
a longer check after pricking out. The 
however, grow more quickly than the t p- 
stunted plants in heated soil which, , 
‘'sixties^’ pots, appeared to 
poorer than those in untreated soil, have . 
infrequently been found to 
better roots when knocked out. ^ 
to which these effects show depends on ^ 
sesaon, the light, the soil, etc., 
have not yet learnt how to 
sometimes they pass so quickly ^hat tn 
hardly observable. In any case, they 
not cause anxiety, for the retardation ^ 
soon after the s^ond leaves are out 
great increase in growth sets ^ ^ 
ing the plants well ahead of those 
treated soils. 
_ (To be continued.) 
An ingenious modification oaneiets 
implement like a comb with three 1€^ 
^ing- blocked up and the ^^der« ^ 
before. This can he hauled out of the bo 
readily than the gridiron. 
