OF THE SAP OF PLANTS. 233 



Cliemical analysis sliowcil that this sap consisted of 99 parts of 

 pure water with one part of dissolved solid matter. Eleven-twelfths 

 of the latter was sugar. Besides sugar, which occurred in this sap 

 to the extent of 616 grains, nearly an ounce and a half, per gallon, 

 there were present a mere trace of mucilage ; no starch ; no tannin ; 

 3\ grains per gallon of ammoniacal salts yielding 10 per cent, of 

 nitrogen ; 3 grains of albumenoid matter yielding 10 per cent, of 

 nitrogen ; a distinct trace of nitrites ; 7*4 grains of nitrates con- 

 taining 1 7 per cent, of nitrogen ; no chlorides, or the merest trace ; 

 no sulphates ; no sodium salts ; a little of potassium salts ; much 

 phosphate and organic salts of calcium ; and some similar magnesian 

 compounds. These calcareous and magnesian substances yielded 

 an ash when the sap was evaporated to dryness and the sugar and 

 other organic matter burnt away, the amount of this residual 

 mineral matter being exactly 50 grains per gallon. The sap con- 

 tained no peroxide of hydrogen. It was faintly if at all acid. 

 Exposed to the air, it soon swarmed with bacteria, its sugar being 

 changed to alcohol, and this again in a few days to acetic 

 acid. The birch-sap had changed to birch- wine and then to birch- 

 vinegar. 



It is noteworthy that the sap when drawn contained a ferment 

 capable of transforming starch into sugar. Two former students of 

 mine, Messrs. Dunstan and Dimmock, who have devised a method 

 of ascertaining the power of such ferments, were good enough to 

 apply their process to some of my sap. They found that one gallon 

 would convert into sugar 21 grains of dry starch, the latter being 

 first gelatinised. Here probably we get an idea of the methods 

 which nature employs in converting one substance into another 

 during the synthetical process or growth, and during the analytical 

 process or more or less rapid decay or combustion of plants. Future 

 investigation in physiological botany will doubtless include much 

 experimenting with ferments. It is an extremely interesting branch 

 of study. The action is well illustrated in the conversion of starch 

 into gum, sugar, etc., during the germination of barley in the 

 manufacture of malt. 



Shortly, respecting the composition of this sap, I may state to 

 the general members of a Natural History Society without risking 

 the dignity of my subject, that a teaspoonful or two of, say, apple- 

 juice, and a tablespoonful of sugar put into a gallon of such rather 

 hard well-water as we have in our chalky district, would very fairly 

 represent this specimen of the sap of the silver birch. Indeed in 

 the phraseology of a water-analyst, I may say that the sap itself 

 had 25 degrees of total, permanent hardness. 



How long the tree would continue to yield such a flow of sap I 

 cannot say. Probably until the store of sugar it manufactured last 

 summer to feed its young buds this spring was exhausted. Even 

 within 48 hours the sugar slightly diminished in proportion in the 

 fluid, the specific gravity going down from 1004-92 to 1004'38. 



And now with regard to the physics of the matter. What causes 

 this outflow ? Or, to put the larger question at once, what causes 



