42 



TIMBER AND TIMBER TREES. 



[chap. 



We thus find the woody layers gradually assuming a 

 tapering or conical form (Fig. 6), and elongating them- 

 selves year by year, so that a large 

 proportion of those visible at the 

 butt are traceable at the upper part 

 of the stem. 



It is very generally admitted 

 that, in latitudes having the sea- 

 sons clearly defined as they are in 

 this country, each circle of lignified 

 wood-tissue is completed in one 

 year, but opinions differ as to this 

 being the case in tropical climates, 

 and there are botanists who con- 

 sider that as many as three or four 

 layers are formed in those regions 

 in the same period of time. Rely- 

 ing, however, on the generally re- 

 cognised rule, of one circle or layer 

 for each year's growth, we have a 

 measure and guide for computing 

 the age of a tree at the time of 

 felling it. Of course, this can only 

 be done with trees having clearly 

 defined concentric circles ; in the 

 instances exceptional to this, we, 

 of necessity, have to fall back upon 

 historical or traditional records to 

 satisfy our inquiries. 



It may be interesting here to 



FIG. 6. note the size and age which some 



species of trees attain. It has been 



said that specimens of the " Baobab " of Senegal are 



more than S,ooo years old, and that some of them have a 



