SANIES. A thin, foetid discharge from sores.
SAP. The circulation of the sap of plants has been the cause of many elaborate theories, each of which in turn has been exploded. Indeed, hut little is really known of the precise causes acting in this abstruse problem. Prof. Burrill, of the Illinois Industrial University, who has given much patient attention to the subject of vegetable physiology, (see Vegetable Physiology,) in a lecture before the Illinois Hor ticultural Society, in relation to sap, stated as follows: The movements and office of sap in the plant have always been interesting topics in vegetable physiology. The physicist, observ ing the rise bf fluids through small tubes what is called capillary attraction and being also acquainted with the force exerted by liquids of different densities through membranes, (called osmosis,) readily satisfies himself that these are sufficient to account for the rise of the sap in the woody structure of plants. With his labo ratory experiments to start upon, he soon learns to modify them sufficiently to meet and explain the ordinary indications of motion of fluids in the treq. Now, it is certainly true that these fluids do not move without some kind of mechanical force to cause them to do so. Being lower in organization than the animal, we might naturally suppose that the forces of the inorganic world would have more direct application in the plant than, for instance, in man, yet we believe the blood is propelled through our bodies by a sufficient mechanical (or chemical?) force. Though the vital powers, whatever they are, preside over and cause the contraction of mus cles, the act in itself is a mechanical one, con trolled by the laws, as to limit of power, etc., that apply to dead substances. Without mate rial substance to work through, the will or life force, if that term is more suitable' for us, cair not cause blood or anything else to move through our organs. Then, it is inconceivable that vitality, separate and apart from the laws of matter, can cause the sap to move regularly or irregularly through the plant tissues. There must be some where and somehow a power behind the throne. There must be a reason, and a sufficient one, for water, whose course is usually down hill, to change its direction and flow vigorously upward in spite of the down-hill tendencies of gravitation. Do, however, the physical laws before cited and the others generally advanced meet the case? Does sap move because of capillary attraction, or of osmosis, or of both combined, or from evaporation from the leaves? There are evidences to the contrary. It is found that the fluid passes through the cells and not through tubes, so that the notion of capillary attraction is not consistent with the fact. It is likewise found that two plants, standing side by side, begin to send up from the roots water at very different times and under very different conditions. According to President Clark's experiments at the Massachu setts Agricultural College, each species of tree from which sap flowed, upon puncture had its own time of beginning and maximum. Thus the ,sugar maple begins to flow in October, reaches its maximum about April 1, and ceases about May 1. The black birch begins about the last of March, reaches its maximum the last of April, and ceases about the middle' of May: The grape has similar dates in May 1, May 20 and June 1. These experiments accord with our own common observation as to the differ ence pf leafing in different species, but, it will be noticed, are not parallel with them. The maple is not very forward in showing its leaves in the spring, though ahead of all other trees in the flow of sap from a wound. There are other things of similar import which might be adduced here, but with this alone, how is it possible for us to hold to the idea that osmosis, the term applied to the passage of fluids through mem branes, causes the gorging of the trees in spring time? Neither is it evaporation from the leaves, for at this season of the year there are no leaves. We indeed have reached a partial explanation, but it may as well be confessed that we do not know all about it. The physical laws to which the phenomenon is generally attributed may be in the main the immediate cause, but, if they are controlled and directed by a something else. There is, furthermore, no positive clew to the cause of another motion of the fluids in plants, so far as my information goes; I mean the rotation that takes place in an individual cell. The
plant, indeed, has a maze of motions going on in its tissues, of which we should be totally igno rant were it not for the microscope. It is more than possible that even this instrument has not revealed all to us yet, and that future investiga tors will wonder at our ignorance and blindness. But the practical thing here is to so manage our plants that the movement of sap can take place freely. If we had all the facts, doubtless this could be better done, for it is groping in the dark to find how before we find why. This is evident: if fluids are to pass through cell walls, the thinner the walls are the easier the passage. Then, from what we know of the plant growth, the newer these cells are the better this flow. The movement takes place more freely in a young shoot than in an old trunk, and this is the phil osophy of the rapid growth seen in sprouts from the side of a tree, and is also a good part of the so-called pruning for vigor. A branch once started to growing rapidly nas an advan tage over the less fortunate ones, even though afterward- having an equal supply of food. A plant from a good seed, capable of throwing out a vigorous shoot, will distance its fellow from a smaller seed fur beyond the difference in the food supplied. So, too, when a plant wilts from lack of moisture, the cell structure may be so impaired as to prevent ever after full, healthy action. A tree checked in its growth by transplanting has much more to do than to restore its mang.ed roots. The whole structure has to be surrr,unded with new tissues before the normal action is restored. It is not, then, a simple question in transplanting as to what percentage live, but how well they live and per form the first year the full functions of growth. Why, it may now be asked, all this motion of the fluids upward, downward, sidewise, endwise, and around, repeatedly, the confines of a cell? In the higher animals, there are vessels for a regular and continuous flow, aud until recently it was sup posed the plant juices made a similar circuit from the root to the leaves, through the wood fibers, thence downward through the bark and adjoin ing tissues. But analogy often leads us wrong. While there may still be something in this speci fication of tissues in plants, there is certainly noth ing comparable to the organs of animals. The latter have a double railroad track, so to speak, upon which freight trains pass and repass with out colliding; but the plant gets along, for the most part, with one, switching and backing and jostling, now making time one way, now the other. The change of water and dissolved inor ganic substances into sap is another of the mys teries connected with the physiology of plants; but it is believed, upon good grounds, to be effected only in presence of the chlorophyl or green portion of the plants; hence, the material entering the root must in the main reach the leaves, and of course the immense evaporation from the leaves must be supplied by the root. Here, then, is cause enough for motion and rea son enough for poor growth, when by any means the fluids are not given the fullest freedom. It is true that the materials which enter the root are forthwith changed to some extent, being no longer simply water and earthy salts; but whether the root itself has any power of chang ing these newly attained elements is an open question. Since the root has sometimes different properties from the rest of the plant, it is argued that it does modify the food elements; but if so, it is a very different thing from that which takes place in the leaves. The green tissues, in the sunshine, rend asunder the particles bound by chemical ties, working against their ordinary affinities, and make them over anew. The chemist, in a well equipped laboratory, accom plishes wonderful things, but fails utterly in competition with a leaf. This is the function of plants, the one property that gives them value to 'us, and the one alone that makes them indispensa able to our use, and the one end as well toward which all the motion aud commotion in the structure is directed. Maturing and ripening are only other terms for the completion of this work, and are very different things from simple cessation of growth. A large leaf surface and recent and healthy cell structure are, therefore, the requirements of plant culture.