Santolina—continued. 
S. C, mquarross (squarrose). 
l. slightly hoary. Stem erect. 
S. C. tomentosa (tomentose). fl.-heads larger than peas; in- 
volucre somewhat mealy. 
S. rosmarinifolia (Rosemary-leaved). _jl.-heads globose or hemi- 
spherical; involucral scales highly — sub-carinate, acute. 
August. Z. linear, ~~ acute; lower ones tubercled on the 
margins ; upper ones flat, entire or slightly denticulate at apex. 
Branches straight, erect, one-headed. A. 2ft. South Europe, 
1683. (S. E. B. 62.) 
SANVITALIA (so-called after the Sanvitali family, 
of Parma). Syn. Lorentea. ORD. Composite. A small 
genus (three or four species) of stove or half-hardy, 
annual or perennial herbs, inhabiting the Mexican 
region. Flower-heads yellow or whitish, rather small or 
mediocre, the disk often purplish; ray florets one or 
two-seriate ; involucral bracts in two or three series; 
receptacle flat or convex; achenes glabrous, those of 
the ray having three arms. Leaves all opposite, entire. 
S. procumbens is in cultivation. It is a half-hardy, 
much-branched trailer, thriving in a mixture of light, 
sandy loam and peat, and may be increased by seeds. 
S. procumbens (procumbent). M. hedds small, like those of a 
species of Rudbeckia, having a bright yellow ray and a dark 
disk ; outer achenes of the disk muricated. July. J. ovate, 
entire. Stem — or diffuse. 1798. (B. R. 707.) There 
is also a double-flowered variety. - 
SAP. The fluid that exists in living plants, for the 
most part inclosed in the cells of which they are built 
up. It varies much in composition in different parts of 
the same plant; and the nature of these variations 
must be explained. A plant growing in the soil pushes 
out roots and rootlets, and through them sucks in, 
from the damp earth, a large amount of water. This 
passes into the hairs of the root by gradual absorption, 
carrying with it some mineral compounds, such as com- 
mon salt, phosphates, &c., in solution. These mineral 
substances are present in only very small proportions 
in the solutions; but, in course of time, a considerable 
quantity thus enters the plant, if the substances occur 
in the soil in forms suitable for absorption by plants. 
The water, with its dissolved mineral substances passes 
from the root-hairs into the root, and thence into 
the stem, remaining little changed in composition, and 
bearing the name of Crude Sap. This crude Sap flows 
upwards in the younger (i.e., outer) layers of wood. of 
the stem, and in some plants it is possible to tap 
the stream, and to obtain nearly pure, and quite drink- 
able, water, when a hole is bored deep enough to reach 
_ the young layers of wood. The crude Sap is con- 
veyed to the green parts of the plant; and there, 
especially in the leaves, it undergoes great changes. 
A quantity of the water is given off from the leaves by 
evaporation or transpiration, rendering the solutions 
denser in the leaves than in the stems. But the great 
change brought about in the Sap in the green parts 
of plants consists in the formation in these parts of 
„various substances, of which the most easily detected is 
` starch. This is present in solid grains in the cells con- 
taining the green substance or chlorophyll, when the 
green parts have been exposed for an hour to the action 
daylight or to strong artificial light. Several sub- 
stances, that in composition resemble starch to some 
extent, are formed in the cells containing chlorophyll, 
and some of them remaifi in solution in the cell Sap, 
while others assume a solid form. Obet agente 
sembling protoplasm in general composition, are 
formed ia we — parts of plants, and probably also 
in other parts; and these, too, are often dissolved in 
the Sap. Owing to the loss of water by evaporation, 
and to the addition of these new organic products, the 
Sap becomes “elaborated,” being heavier and thicker 
than the crude Sap. It passes from the parts in which 
it was elaborated to all parts where nourishment is re- 
quired, whether to supply the material consumed during 
ji.-heads smaller than peas. 
. 
AN ENCYCLOPÆDIA OF HORTICULTURE. 
357 
Sap—continued. a 
growth, or to allow of the formation of new structures 
at the growing points of stems, and in the growth of 
leaves, flowers, and fruits. In many perennial plants, 
a large proportion of the new products is also trans- 
ferred from the leaves to the stems, or to underground 
store-houses, e.g., tubers of Potato, roots of Parsnip 
and Turnip, bulb-seales of Lilies, &c} There are thus 
descending currents of elaborated Sap, in Dicotyledons, 
usually outside of the ascending currents of crude Sap. 
The elaborated Sap descends by two chief routes: the 
first, down which pass dissolved starch and compounds 
of a similar kind, is believed to be through the cellular 
tissues of the bark, and, to some extent, the medullary | 
rays and the pith; the second route, down which the 
protoplasmic substance passes, is believed to be the 
soft-bast, or innermost layer of the bark. Down this the 
IG: 415, A, SAPERDA POPULNEA, natural size; B, BRANCH OF 
gi eye showing Ravages committed by the Insect. (Page 358.) 
latter stream’ flows, especially by means of the “ sieve- 
tubes” — slender tubes of long cells, end to end, that 
are separated, only partially, by sieve-like cross walls, 
the openings in which allow the protoplasm to pass from 
cell to cell. A practical result of the situation of the 
descending current is that if a ring of bark is removed, 
or a tight ring of any material (e.g, wire) is bound — 
round a branch of any Dicotyledon of ordinary structure 
(é.g., an Apple-tree), the elaborated Sap is prevented 
from passing downwards; a thickened border is produced 
above the obstruction, and the crop of fruit on the 
- branch is increased, since it gets all the food produced | 
in the leaves of the branch, while duly supplied with 
