ON STEMS. 47 



' H 



in woods of a lighter color, but it is always sufficiently so 

 to be distinguishable. Look at this trunk of chesnut-tree, 

 which has been recently cut down with a saw. 



Caroline. I not only see plainly where the perfect 

 wood is separated from the alburnum, but I can distin- 

 guish every layer of wood. I follow them in imagina- 

 tion in their successive shoots upwards to extricate them- 

 selves from the pressure of the new layers, by counting 

 the number of layers at the base of the tree ; then, Mrs. 

 B., shall I be able to ascertain its age ? 



Mrs. B. Yes ; and you may do more : for if you take 

 the trouble to count the number of layers at each end of 

 one of those pieces of wood which have been sawed into 

 logs for fuel, you will learn how many years that portion 

 of the tree was in growing. 



Emily. There are thirty layers at one end, and twen- 

 ty at the other ; consequently the tree must have been 

 ten years growing the length of this log. I little thought I 

 could ever have taken so much interest in a log of fire-wood. 



Mrs. B. However mean or common-place may be the 

 purposes to which we apply the works of nature, when 

 studied in a philosophical point of view, they are no less 

 objects of interest and admiration. 



The annual layers of wood are distinguishable not only 

 by their different degrees of hardness and density, but also 

 by their being separated by layers of the cellular system ; 

 so that, when you examine the trunk of a tree, you per- 

 ceive zones of woody fibre and zones of the cellular system. 



Emily. Can the age of endogenous plants be ascer- 

 tained in the same manner ? 



Mrs. B. No ; the annual layers of wood are not suffi- 

 ciently distinct from each other. 



Caroline. But the rings annually formed by the vesti- 

 ges of leaves is a still better record of their age, for it is 

 not necessary to cut down the tree in order to ascertain it. 



Mrs. B. For a certain period they may answer this 

 purpose ; but these vestiges are obliterated by time, and 



228. How may it be ascertained how many years a tree has been 

 growing 1 ? 229. What fact does Emily learn from the log of wood, 

 which has twenty layers at one end and thirty at the other 1 ? 230. What 

 moral reflection does Mrs. B. here make'? 231. How are the differ- 

 ent layers of wood further distinguishable 1 ? 232. Can the age of en r 

 dogenous plants be ascertained in the same way! 233. Why may it 

 not be done by the rings annually formed by the vestiges of leaves'? 



