An Encyclopedia of Horticulture. 



357 



Santolina — continued. 

 S, C. squarrosa (squarrose). Ji.-hi'aclx smallei- than peas. 



/. Hli;;litly lioary. Stem erect. 

 S. C. tomentosa (tomentose). !i. -heads larger than peas ; in- 



voUlcre somewhat mealy. 

 S. rosmarinifolia (U«.iseiiiar\ -leaved), jl. -heads j^lulioso or hemi- 



sitluTical ; invuhicial ,sc:i.le- lii;ilily glabrous, sub-carinate, acute. 



Auf;ust. I. linear, .sli.i^htly acute ; lower ones tuberded on the 



mariiins : upper ones tlat, "entire or slightly denticulate at apex. 



Branches straight, erect, one-headed, h. 2ft. South Europe, 



1683. (S. E. B. 62.) 



SANVITAIiIA (so-called after the Sanritali family, 

 of Parma). Syn. Lorentea. Ord. ComposUn;. 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. procumbent: 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 (pr^icumbent). Ji. -heads small, like those of a 

 species of liudbeeh-ia, having a bright yellow ray and a dark 

 disk ; outer achenes of the disk muricated. July. L ovate, 

 entire. Stem procumbent or dlffu.se. 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 difl'erent 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 jiresent 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 Cncde 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 jjarts 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 

 of 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 remain in solution in the cell Sap, 

 while others assume a solid form. Other substances, re- 

 sembling protoplasm in general composition, are also 

 formed in the green 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 enrde 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 



Sap — contimted. 

 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-scales 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 

 flrst, down which pass dissolved starch and compounds 

 of a similar kind, is believed to be thi-ough 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 



Fig. 415. A, S.4PERU1 ropi:LNEA, natural size; B, Branch op 

 Poplar, showing Ravages connnitted by the Insect. (Page 358.) 



latter stream flows, especially by means of the " sieve- 

 tubes ' — slender tubes of long colls, 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.y.. wire) is bound 

 round a branch of any Dicotyledon of ordinary structure 

 {e.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 



