204 ANNUAL REPORT. 



referred to by Mr. Underwood. It struck me at once as illustra- 

 ting an interesting fact in regard to the sap. In the winter the 

 sap does not travel up and down the tree like it would in a 

 stream, for it cannot come from the roots in cold weather. There 

 is in a maple tree a large amount of sap and a considerable 

 quantity of air. During a cold night the air passes in and out 

 of the tree, for you know that air will pass right through a tree, 

 but of course it is very slowly. There is a certain quantity of 

 sap there and air within the cells. When the bright sun comes 

 out, the heat striking the tree expands the air, that squeezes 

 the sap in all directions. If you tap the tree the sap flows out; 

 that is the theory of the flow of sap in the spring. Had the fire 

 been built up very slowly, the tree would have been heated 

 slowly and the air would have gradually passed out and that 

 phenomenon would not have been noticed. 



Mr. Underwood. I don't see how that would affect the tree in 

 that way in the winter. 



Mr. Pearce. I would like to say one word on that subject. I 

 am glad the professor is here, so if I am wrong he can correct 

 me. I take a different view of this injury to the tree from all 

 others pretty much, but science has to bring out these points; 

 theory is not going to do it. It is a well known fact that during 

 the winter time the roots are inactive, but there is life in the tree. 

 In the spring of the year the buds begin to start, through the aid 

 of the carbon in the air, and that produces sugar and glucose and 

 other substances necessary ,to produce the bud. Under the bark 

 of the tree the sap cells are supplied with food, which during the 

 coldest days of winter, is passing off through the pores of the 

 tree to the outside. There is food in the tree passing off all the 

 time. If the winter is very long and the supply is very scant 

 this food become entirely exhausted. I have investigated this 

 with a microscope that magnified two or three hundred diame- 

 ters. When the food in the tree becomes exhausted, I find the 

 bark dies and becomes dried up. As long as there was this 

 nourishment it kept the bark alive and kept it healthy; but just 

 the moment all the food in the bark passed out, there was noth- 

 ing to keep up the freshness and vigor of that bark. We see this 

 illustrated with the southern trees, where they have shorter win- 

 ters, and of course there it requires less food to carry them 

 through. There is food enough to last two or three months. 

 But here we find sometimes that there is not enough food in the 

 trees to carry them through, and they become exhausted some- 



