310 



INTRODUCTION TO BOTANY 



the early spring growth of new parts of the plant or in re- 

 plenishing old parts, or may even be retained until another 

 year. The passage of sugar-laden sap is through the youngest 

 fibrovascular bundles. By boring a hole through the dead 

 bark into this region, sap may be withdrawn. When it is se- 

 cured in sufficiently large quantities, the water may be evap- 

 orated from it until thick sirup or sugar remains. Ordinarily 



FIG. 233. Sugar-maple trees which have been tapped every year for over 



eighty years 



The trees are tapped by boring into them so as to reach the sapwood ; then a tubu- 

 lar spile is driven into the hole, and a bucket is suspended upon a hook on the 

 spile. In this way the sap is caught in the bucket 



a good sugar-maple tree produces 15 or 20 gallons of sap 

 in one season, though this amount may be greatly exceeded 

 by especially good trees. The percentage of sugar in the sap 

 varies widely in different seasons and between different trees 

 in the same season, but usually it is from 2 to 3 per cent. 

 Individual trees produce in one season from half a pound to 7 

 or 8 pounds of sugar. Maple sirup is the partially evaporated 



