124 



Ages of trees Exogens. 



is to a tree what blood is to an animal, and both 

 the sap and blood are always in circulation. 



123. Leaves not only inhale (breathe in) moisture, but 

 they also exhale (breathe out; it. Some of the water 

 which has brought up the nourishment to the leaves, 

 being no longer required, is thus exhaled or evaporated 

 through the pores of the leaves. 



124. Does the apple tree enlarge on the in- 

 side, or outside ; by the rising, or the returning 

 sap? The increase is on the outside of the 

 hard wood, or just along the inner bark, and 

 is supplied by the returning sap. 



125. Every year a layer is added; therefore, 

 when such a tree is sawed across the trunk, the 



layers will appear like 

 rings and show the age 

 of the tree. 



126. In counting the rings, 

 the pith (i) and the bark (4), 

 belonging to the first year's 

 growth, are not to be in- 



Section of an Exog-en of two Cmded. 



years' growth. ,_ , . , . 



127. Trees which thus 



grow by additions to the outside of the hard 

 wood, or externally, are called exogens (ex'-o- 

 jens) ; such include apple, pear, maple, elm, 

 and many other kinds of trees. 



1 28. Trees and plants which increase by inter- 

 nal growth, showing no layers or rings like those 



