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THE DICTIONARY OF GARDENING, 
SUBMERGED, SUBMERSED. Growing under 
water. 
SUB-PETIOLAR. Beneath the petiole. 
SUBSOIL. The layer of soil existing at such a 
depth below the surface that it is not reached in the 
usual operations of gardening and agriculture, i.e., from 
about lft. below the surface downwards. In some 
localities, the Subsoil is of almost the same composition 
as the soil; but there is usually a considerable difference 
between them. Nor is it difficult to understand why this 
should be the case, in so far, at least, as regards the 
proportion of organic matter, and of the soluble foods 
of plants, in each; for plants draw a large share of 
their nourishment from the surface soil, and thus im- 
poverish it of the substances used by them. On the 
other hand, such plants as die and decay on any piece 
of ground increase the proportion of organic matter in 
the surface soil, but add little, if any, to the Subsoil. 
The physical texture of the surface soil is also rendered 
more open by the numerous roots that traverse it; and 
this greater looseness is much increased by the operations 
of cultivation. The freer access of air and rain thus 
afforded permits a more rapid decomposition of the soil. 
The looser texture also permits rain-water to trickle 
down till it reaches the Subsoil, carrying with it soluble 
compounds out of the surface soil. If the Subsoil is clay, 
it retains what is carried down in this way, whether 
such additions are useful as food for plants, or poisonous 
to them. Hence, the Subsoil may become rich, so as to 
yield excellent crops when exposed to air and light; 
or it may be almost barren until the poisonous sub- 
stances in it (e.g., Oxides of Iron) have been changed, 
by the action of natural agents, such as air and rain, 
or by the operations of agriculture, into harmless com- 
pounds. : : 
-> The nature of the Subsoil exercises a very important 
influence on the fertility of the surface soil. If it is 
open and sandy, it allows the rain-water to drain away 
rapidly; hence, there is no reserve, in times of drought, 
to supply the place of that evaporated from the surface 
-of the soil, and from the plants thereon, which suffer in 
their growth, or perish for lack of water. If, on the 
other hand, the Subsoil is clay impervious to water, the 
rain is caught, and collects in hollows, where it stag- 
nates, with the usual ill-consequences of the surface soil 
becoming saturated and cold, and being rendered sour 
by the formation in it of organic acids, from the action 
of the water on decaying plant-remains. Clay Subsoils 
must, therefore, be broken up by the Subsoil plough, 
or by the spade and fork; but they should be well 
drained about one or two years before they are broken 
up, as wet clay coheres very quickly if merely cut 
through. Excellent results often follow the bringing of 
the Subsoil to the surface, by means of Subsoil ploughs 
or spades; and it is evident, from what is said above, 
_ that it must be an advantage to bring within reach of 
the roots of plants new soil, richly supplied with sub- 
stances required by them, and that have been used up, 
to some extent, in the surface soil. Moreover, the new 
soil, when exposed to the atmosphere and frost, breaks 
up, and affords new food supplies, in addition to those 
washed into it by rain from the higher layers. 
Where the Subsoil contains poisonous substances, it 
should not be disturbed, unless it is possible to let the 
ground lie fallow for a year or more. In this time, the 
danger will probably be removed by the action of the 
atmosphere upon the hurtful substances. To ascertain 
whether the Subsoil is hurtful, the following method has 
been employed : A flower-pot is filled with the Subsoil 
to be tried, and another is filled with ordinary soil, for 
comparison of results. Seed of the same kind is sown 
in both, and, if the Subsoil gives a good crop, this shows 
it to be safe, and worth bringing to the surface; but, 
Subsoil—continued. 
if the crop is sickly and weak in the Subsoil, while 
good in the other pot, the Subsoil is evidently un- 
wholesome in its natural state, though it may be 
rendered fertile by exposure, for a time, on the surface. 
SUB-SPECIES. A rank higher than that of Variety, 
but lower than that of Species. 
SUB-TROPICAL GARDEN. A term applied to 
a portion of a flower garden or pleasure-ground devoted, 
during summer, to stately-habited foliage plants, which 
are arranged with a view to represent tropical vegetation. 
Many of the plants used are natives of tropical countries, 
and are, consequently, only available for placing outside 
during the hottest part of the year; but there are others 
of stately aspect which are quite hardy, and are invaluable 
for associating with them. Tropical plants of slow growth, 
which have to be kept under glass all the winter, re- 
quire a great deal more space than can generally be 
afforded them; and as they are also very expensive sub- - 
jects to procure in the first place, comparatively few 
gardeners have any at their command, One of the most 
important provisions for sub-tropical plants is shelter; 
their leaves in most instances are soon torn, and the 
plants disfigured, if exposed to rough winds. Shade and 
moisture are also necessary for many Tree and other 
Ferns and Cycads. There are numerous sub-tropical 
plants which may readily be raised from seed each spring, 
as they are quick-growing, and form quite large specimens 
before autumn, when planted out about the middle of 
June, in rich soil. Of these Albizzia lophantha, Castor- 
oil plants (Ricinus) in variety, Nicotianas, Solanums, 
Wigandias, and varieties of Zea are specially valuable. 
Cannas, too, may readily be raised from seeds in spring; 
but the plants are nearly hardy, and may afterwards be 
increased by division of the rootstock in spring. Of 
tropical plants the most serviceable are: amongst Palms 
—Chamerops humilis, Livistona australis, L. chinensis, 
Phenix dactylifera, Ptychosperma Cunninghamiana (often 
known in gardens as Seaforthia elegans), Trachycarpus 
excelsus and T. Fortunei. Musas—M. Ensete and M. 
superba. Tree Ferns—Alsophila australis and A. excelsa, 
Cyathea dealbata, Dicksonia antarctica. Cycas circinalis 
and (. revoluta may be plunged in sheltered positions 
along with the plants above-mentioned. Amongst other 
subjects also available are Arundinarias, Bambusas, Cen- 
taureas, Cordylines, Erythrinas, Fatsias, three or four 
species of Ficus, Funkias, the’ New Zealand Flax (Phor- 
mium. tenax), Pampas Grass, &c. Other remarks on this 
subject will be found under Garden, and the descriptions 
and culture of plants referred to are given under their 
respective headings. 
SUBULARIA (from subula, an awl; alluding to the 
form of the leaves). Awlwort. ORD. Crucifere. A mono- 
typic genus. The species, S. aquatica, is an annual, 
aquatic herb, indigenous in Europe (Britain), Siberia, 
and North America. It has no value as a garden subject. 
SUBULATE, SUBULIFORM. Awl-shaped. 
SUCCISA. Included under Cephalaria and Scabiosa. 
+ Rate Abruptly cut or broken off at the lower 
end. 
SUCCORY. Another name for Chicory (which see). 
SUCCOVIA (named after Professor Geo. Suckow 
1751-1813, a botanist of Heidelberg). ORD. Cruciferae. 
A monotypic genus. The species, S. balearica, an annual, 
with yellow flowers and pinnatisect leaves, native of the 
Canary Islands and the Mediterranean \region, is pro- 
bably not now in cultivation. > 
SUCCUBOUS. When, in leaves crowded on a stem, 
the base of each leaf covers the apex of the next below. 
SUCCULENT. Very cellular and juicy. 
