STRUCTURE.] 



UNSAFE GUIDES TO AGE. 



201 



they are so confounded, that there is not the slightest trace 

 of annual separation. It is also to be remarked, that in 

 Zamias we seldom find more than two or three zones of wood, 

 whatever may be the age of the individual ; and yet it appears 

 from Eeklon's observations, that a Zamk, with a trunk only 

 four or five feet high, can scarcely be less than two or three 

 hundred years old. (Lehm. Pugill. vi.) According to Decaisne 

 (Comptes rendus, v. 393.) the zones of wood in Menisper- 

 mads each result from the growth of several years. More- 

 over it is certain that in tropical countries some trees will 

 form from one to four well defined zones of wood during the 

 growth of a single twelvemonth. 



With regard to judging of the age of a tree by the 

 inspection of a fragment, the diameter of the stem being 

 known, a little reflection will show that this is to be done 

 with great caution, and that it is liable to excessive error. 

 If, indeed, the zones upon both sides of a tree were always 

 of the same, or nearly the same thickness, much error would, 

 perhaps, not attend such an investigation; but it happens 

 that, from various causes, there is often a great difference 

 between the growth of the two sides, and consequently, that 

 a fragment taken from either side must necessarily lead to 

 the falsest inferences. For example, I have now before me 

 four specimens of wood, taken almost at hazard from among 

 a fine collection, for which I am indebted to the munificence 

 of the East India Company. The measurements of either 

 side, and their age, as indicated by the number of zones they 

 comprehend, are as follows : 



Now, in the first of these cases, suppose that a portion of the 

 side A. were examined, the observer would find that each 

 zone is 0*225 of a line deep ; and, as the whole diameter of 

 the stem is 15 lines, he would estimate the side he examined 



