Show NORMAL DEPARTMENT Sap and How it loves noves ANY question relating to life is always interesting and since we we are beginning to suspect that there is a grand unity of life the lower forms of animal and vegetable vegetable vegetable life are invested with a new and deeper interest This interest sometimes becomes so deep that enthusiastic persons are tempted tempt tempt- ed to find resemblances where none really exist This is always to be deprecated deprecated deprecated dep dep- for the unwise enthusiast always injures his cause more than he h helps it The whole course of modern thought and investigation leads us to beli believe ve that animal and vegetable life are one oneat oneat oneat at the very base that is that there is no essential difference between the manner manner manner man man- ner of growth and the reproduction of f an animal and a vegetable cell but that does not mean that the internal economy of that great aggregate of cells which we call calla a horse is necessarily the same as that in inthe inthe inthe the aggregate of cells which we call a horse Some writers in their eagerness eagerness eager eager- ness liese ness to demonstrate the unity of animal and vegetable life have tried to show that even in the matter of circulation there is a striking similarity b between tween plants and animals that the sap of the plant corresponds to the blood of the animal and that just as the blood of the higher animal i is in constant motion and flows t through rough all parts of the body over and andover andover andover over again so the sap of the higher plant is engaged in a continuous motion which results in a true circulation This latter idea I believe to be false and while space forbids an extended argument I still desire to state a few facts which bear directly upon this ques ques- tion It is almost needless to say that in this brief statement of facts I make no claim to originality simply using such facts as are the common property of all readers of recent botanical litera litera- ture The sap of the higher plants is imbibed ed by the root hairs with which the roots of plants become clothed early in inthe inthe inthe the spring before the leaves appear and which usually perish after the tree or herb has lost its leaves in the fall Carefully conducted conduct d experiments show that the force with which the rootlets absorb water is very considerable usually usually usually us us- much greater than the force which is expended in simply raising the water from the roots to the top of the plant This will necessarily result in an outward outward outward out out- ward pressure of the sap within the tree As the power of the root h hairs irs to absorb is increased by warmth and diminished by cold it follows that the 1 internal pressure of the sap must be subject to c continual variation During the summer while the tree is lis clothed with leaves the evaporation through their stomata is so rapid that the internal internal internal inter inter- j nal pressure never or at most very seldom seldom sel sel- eldom dom rises to any considerable degree but when the leaves are shed in the fall and the only loss the plant can sustain is through its bark the pressure rapidly rises for the plant becomes surcharged with sap and this condition usually lasts all winter though the pressure grows less toward spring because during during during dur dur- ing the greater part of the winter the routs roots are without root-hairs root and so little or no absorption takes place and a little evaporation continually takes place through the bark of the trunk and branches Early in the fall just after the leaves are shed the sap pressure may become so high that if the tree is wounded in any part of its body the sap will flow out through this wound This outward flow of sap is called bleeding bleeding bleeding bleed ing II As the root hairs are developed before the leaves appear in the spring the absorption of water from the earth begins before the plant is in a condition to permit its rapid evaporation This causes high internal pressure of the sap and in some trees like the maple the pressure is sufficient to cause large quantities of sap to flow out through artificial wounds In the maple as in inmany inmany inmany many other trees the process of growth results in the formation of sugar and as the sugar readily d dissolves in th the sap the trees are It tapped II for the purpose of getting this solution to make maple syrup and maple sugar As soon as the leaves of the tree appear the evaporation through them is isso isso isso so ra rapid pid that the pressure quickly falls and the tree ceases to II bleed II Then to too the trees form new tissue so rapidly J that the tissues heal almost as rapidly t f I. I as they are wounded so this quickly checks the outward flow When the ascending sap reaches the leaves under the rhe influence of the sunlight in the presence of chlorophyll or leaf-green leaf it undergoes a marked change from a simple solution of gases and mineral salts in water it becomes elaborated sap or real food for foi plant plan t cells In this condition it is slowly diffused over the entire plant moving up as s well as down but following no well defined channel In tn this brief account of the sap within with in the tree a few points of similarity between the lowest animal forms and plants will be he noted but it will be observed observed observed ob ob- served that between the higher animals and plants there is opportunity for contrast contrast con con rather than comparison C. C A. A Whiting Whiling |