1859. 



NEW ENGLAND FARMER. 



171 



action is the conversion of the crude sap ab- 

 sorbed from the soil by the roots, into the proper 

 juice, for the nourishment and increase of the 

 plant, with its various products. This crude sap 

 consists of water, holding in solution minute 

 quantities of various kinds of solid and gaseous 

 matter derived from the soil. In its passage 

 from the root to the leaves its composition is 

 somewhat modified by dissolving the previously 

 formed secretions, which it meets with on the 

 way. 



ExlialaUon is the process by which the super- 

 abundant waste of the sap is given off to the at- 

 mosphere, so that the remaining sap is reduced, 

 as it were, by concentration, and contains a great- 

 er portion of solid matter. It is much like the 

 perspiration in animals. It is to be distinguished 

 from evaporation ; the latter depending solely 

 upon heat and the state of the air, and being, in 

 plants, almost wholly restrained by the epider- 

 mis or skin of the leaf. 



This exhalation takes place through number- 

 less little mouths on the upper surface of the leaf 

 called stomata, similar to the pores of our skin ; 

 these mouths are opened by the influence of the 

 light, and closed by its absence, and, therefore, 

 exhalation can only proceed in the presence of 

 the light. A sunflower 3i feet high, was ascer- 

 tained by Hales to transpire or send off from 

 20 to 30 ounces of water daily. 



Absorption is chiefly performed by the roots of 

 plants, but when the roots are imperfect, it is ev- 

 ident that the plant must derive its nourishment 

 mostly from the absorption performed by the 

 leaves. Every one knows how plants, when 

 parched and withered by drought, are raised by 

 a shower which does not reach their roots, but 

 only moistens their leaves, as you must have no- 

 ticed in your corn-fields many times, how rapidly 

 the parched and rolled blades of corn will unfold 

 themselves and assume a lively green, even un- 

 der a slight shower that could not reach the roots. 

 The under surface of the leaf absorbs, and the 

 upper exhales. Wonderful arrangement ! 



Respiration in plants is much like the breath- 

 ing in animals. It is equally constant and equal- 

 ly necessary. It is performed principally by the 

 leaves, and consists of the absorption of oxygen 

 from the atmosphere, accompanied by the rejec- 

 tion of carbonic acid. It appears to be going on 

 constantly during the life of the plant, and the 

 result is the removal of a certain superfluous 

 portion of carbon, in a state of combustion with 

 oxygen, from the nutritive substance of the plant, 

 just as the same deleterious acid is removed 

 from the blood of animals by breathing. 



Digestion in plants consists properly of all 

 those changes efl'ected by the leaves in rendering 

 the crude sap fit for the purposes of nidrition. 



This consists in the decomposition of carbonic 

 acid by the green tissues of the leaves, under the 

 stimulus of the light, the fixing of the solid car- 

 bon and the evolution of the pure oxygen. 



Several things present themselves to our mind 

 by which we might illustrate these points, — but 

 it seems to us that the careful reader will now 

 see some of the physiological operations of the 

 tree which he is about to prune. He cannot 

 have failed to see that soon after the middle of 

 March, varying a little with varying seasons — 

 the sap, then more like water than anything else, 

 ascends the stem of the tree and reaches the ex- 

 tremity of every twig or branch, and that wher- 

 ever any cut or rupture takes place in the pores, 

 the sap will naturally run out. 



But when the sap has reached the leaves it un- 

 dergoes a material change there, — the watery 

 particles being evaporated, and leaving it more 

 solid. This now returns down the tree, not 

 through the sap vessels where it went up, but 

 flows between the bark and the soft, woody sub- 

 stance under it, and pausing on the way and in- 

 creasing the size of the tree. Under these cir- 

 cumstances, if a cut is made into the sap vessels 

 sap does not run from it, because there is little 

 or none there. The wound made at this season, 

 — say from the 15th of June to the middle of Ju- 

 ly, — should be covered with wax, shellac or paint, 

 and the returning sap, now passing down directly 

 under the bark, will push oid the new, green bark 

 around and over it, if not too large, and entirely 

 covers it the first season! 



If, on the contrary, the wound bleeds, that is, 

 the sap runs out, it flows down the outside of the 

 limbs or trunk of the tree, undergoes a chemical 

 change as it becomes exposed to the atmosphere, 

 leaves long, black lines on tlie surface which so.jh 

 kills the bark, and the tree eventually dies ! 



It may not be that the tree perishes from t' is 

 poison alone, but from the want of proper actio. i, 

 as in the case, sometimes, of the amputation ot 

 an arm, the muscles on that side contract, the 

 chest falls away, and in some instances the luDgs 

 are seriously affected ; and this results, we sup- 

 pose, from a want of proper action, after an im- 

 portant member has been taken away. 



It seems to us that the reasons now given for 

 June and July pruning, ought to have weight, 

 and we think they will, if carefully considered. 



We have occupied considerable space in repiy 

 to our correspondent, because the subject is one 

 of importance to the farming interest. We give, 

 below, an article long since received from anoth- 

 er correspondent on the same topic. 



BLACK SPOTS ON APPLE TREES. 



I have noticed in the New England Farmer 

 remarks made in regard to a blight, or large, 

 black spots which come on the trunks and limbs 



