434 
THE DICTIONARY 
OF GARDENING, 
Silica—continued. 
access to the roots of plants contains an appreciable 
amount of Silica, either pure or, more frequently, com- 
bined with alkalies. Silica exhibits the properties of a 
weak acid, in its power of combining with various metals. 
It combines with these, in more than one proportion, 
certain compounds, called normal or basic Silicates, con- 
taining a larger proportion of the alkali than do the 
others. These normal Silicates are the ones that dissolve 
in water. 
Silicates (especially normal Potassic Silicate) pass into 
the root-hairs of the plants from the soil, dissolved in 
the water absorbed by the hairs, and are then carried 
up the stems, as described under Sap. They are 
easily broken up by the acids formed in plants during 
growth, e.g., Oxalic and Citric Acid, &c.: the metals com- 
bine with these acids to form new compounds, and the 
Silica is set free in the cell-sap; but, not being so soluble 
as the Silicates, it is mostly added to the walls of the 
cells, and is peculiarly often found in the layer or cuticle 
on the outer surface of the stems or leaves. In some 
plants, this layer is so strong and continuous that all 
the vegetable substance may be destroyed by means of 
Nitrie Acid, or by burning on platinum-foil over a spirit- 
lamp, without destroying the continuity and markings of 
the cuticle, which even extends over the hairs. Such a 
deposit of Silica in the epidermis is well shown in many 
grasses, and still better in the Horsetails or Equiseta; 
but it is met with also in many other plants, e.g., in 
Deutzia scabra, where it forms a beautiful object when 
all the vegetable matter in the cuticle has been destroyed. 
The use of Silica to plants is very doubtful. It is pre- 
sent in the ash of almost all plants. In many it is so 
abundant as to seem of much importance to them; yet 
the results of experiments on growing plants in artificial 
soils from which it is almost absent, tend to the 
conclusion that the growth of plants is not greatly in- 
terfered with even when the supply of Silica taken in 
by them is far below that usually present in them. For 
example, the straw of grasses is usually very rich in 
Silica (frequently to the amount of one-half of the ash) 
when grown in ordinary soils; yet grasses grown in 
artificial soils, from which it has been excluded as com- 
pletely as possible, and whose ash, in consequence, con- 
tains less than 1 per cent. of Silica, prove as healthy 
and vigorous in every way as if they had been grown in 
ordinary soils. Probably, a large proportion of the Silica 
is absorbed in the form of alkaline Silicates, as men- 
tioned above; and the Silica remains as a deposit in 
the cell walls after the alkalies have been made use of 
in the nutrition of the plants. It has been suggested 
that Silica may be of service in two ways, viz., in giving 
strength and rigidity to the stems, and in rendering the 
euticle harder, so that when spores of parasitic Fungi 
fall upon it, and begin to germinate, the mycelium tubes 
find greater difficulty in piercing into the tissnes of the 
plants. The Silica in the cuticle may thus be a de- 
fence against disease from this cause, but, necessarily, 
against only such Fungi as bore through the cuticle 
into the inner tissues, and not against those which 
push in their mycelium through stomata. 
SILICATES. See Silica. 
SILICLE. A siliqua as broad as it 
- broader, 
is long, or 
SILICULOSA. A Linnean artificial order of the 
class Tetradynamia, having siliculose pods. 
SILIQUA. The long, pod-like fruit of Crucifere. It 
consists of a pair of valves applied to a frame on which 
the seeds grow. 
SILIQUOSA. A Linnean artificial order of Tetra- 
dynamia, having siliquose fruit. 
SILK. TREE. A common name f 
genera Bombar and Eriodendron. pin 
| wing, which is notched at the top. Leaves alternate. 
SILKEN SISSY. An old name for Asclepias. 
SILK-TREE. A common name for Albizzia Juli- 
brissin. 
SILK VINE. A common name for Periploca greca. 
SILKWOOD-TREE. A name applied to Muntingia 
Calabura. 
SILKY. See Sericeous. 
SILKY OAK. A popular name for Grevillea robusta. 
SILPHA. A genus of Beetles, the larve of which 
usually feed in the rotting bodies of animals, and are 
especially numerous in dead moles, birds, and other so- 
called “ vermin,” hung up as scarecrows. The insects 
of this genus are, for the most part, considerably de- 
pressed or flattened from above downwards, oval in 
outline, about 3in. or 3in. long, with a small head, and 
furrowed wing-cases. They are almost entirely black, or 
brown-black, with a dull yellowish, downy coating, which 
is easily rubbed off. The grubs are more slender in 
form than the adult insects, and all the rings, except 
the three next the head, have the edges sharp, and pro- 
longed forward into a tooth, and the tail ends in two 
sharp points. They are usually entirely black, or black 
with a narrow, tawny border. They are active in their 
habits, running about by means of three pairs of short 
but well-formed legs, situated on the front part of the 
body. When full-fed, they form cocoons in the soil, in 
which they become pupæ, and in due time beetles As 
long ago as 1844, larve of a Silpha were found feeding 
on Beets, in France; and in the same year they proved 
seriously injurious to Mangel-Wurzel crops near London- 
derry, in Ireland. They devoured the young leaves 
almost as soon as the latter appeared, till only the larger 
ribs remained, and the plants, in consequence, died off 
largely. Mangel-Wurzel and Beets alone suffered ; and 
such crops as Oats, Wheat, Potatoes, and Turnips escaped 
unharmed in fields where the former plants were entirely 
destroyed. From larve feeding on Beets, in France, 
there were reared beetles belonging to the species — 
S. opaca, known as the Beet Carrion Beetle ; and the 
same insect was also identified as the culprit in Ireland. 
It is rather under jin. long, flattened, and brownish- 
black, with the tip of the body dull red. There are- 
three ridges down each wing-case. This beetle had long 
been known to frequent dead bodies of animals. It is 
probable that other species of Silpha also injure Beets 
and other garden produce. 
Treatment. For the sake of prevention, only manure 
free from such substances (e.g., offal) as might attract 
the beetles should be used for ground on which Beets 
and Mangel-Wurzel are to be grown. Should the plants 
be attacked, dressings of gas-lime and of sulphur or soot, 
scattered over the wet leaves in dewy mornings, would- 
probably be of service in checking the evil, as would 
also be paraffin dressings. All methods of strengthening 
the plants and promoting the growth of new leaves are, 
of great importance, and manures may enable the crops 
to pass through an attack without serious results. . 
should the attack prove fatal, it will be well to utilise 
the ground for some other crop, which may be sown or 
planted with safety in the infested soil immediately 
after the removal of the Beets or Mangolds. 3 
Í (Silphion, the ancient Greek name used by 
Hippocrates for a plant which produced some gum-resin, 
perhaps asafœtida, and which was transferred by Linnæus 
to this genus). Rosin-plant. ORD. Composite. A genus 
consisting of eleven species of tall, coarse, hardy, peren 
re herbs, with a copious resinous juice, confined to- 
North America, Flower-heads yellow, large, corymbose- 
reese involucre broad and rather flat the scales 
rt ihe to m many rows; ray florets numerous, fertile; 
sk florets sterile; achenes glabrous, surrounded by a 
