518 NATURAL HISTORY. 



fused together, no change of colour will ensue ; -whereas with strontia, &c., the co- 

 lour is changed to dull grey or brown. And, in like manner, if a baryta salt in 

 powder be simply heated with a drop of a manganese solution, the mass will be 

 coloured blueish-green : the colour in this case, as in the cases mentioned above, 

 arising from the formation of manganate of baryta. 



Book received : — "Figures and Descriptions of Canadian Organic Remains. De- 

 cade III." This important publication, issued by the Geological Survey of Canada, 

 will be noticed in full, in the next number of our Journal. 



E. J. C. 



STATURAL HISTORY. 



AGE OF TREES. 



The following extract from the Gardener's Chronicle, edited by Dr. Lindley, is 

 of considerable interest. If those who cut down large trees in Canada would note 

 the number of rings, with the diameter, or circumference, and the kind of tree, we 

 should soon possess valuable data forjudging of the rate of growth of our trees, 

 such as in a little time could not fail to be found practically useful. 



" Is it possible to judge of the age of an old tree by its circumference ? we do 

 not mean precisely, but with any approach to exactness. Can we, for instance, 

 ascertain the age of a very ancient oak within a century of the truth ? This is a 

 point which seems to us worth investigation. That a tolerably exact inference 

 may be drawn from counting the rings of wood, even such as remain when a tree 

 has become hollow, is well known. But questions constantly arise with reference 

 to standing trees, whose wood-rings of course cannot be examined, and it is to 

 them that we would direct enquiry. 



The only way of arriving at a ceitain conclusion is evidently to determine the 

 average rate of growth of trees of various kinds. Could we, for example, find 

 the average of successive half centuries of groAvth, extending over any long period 

 of time, the method of computation would be obvious. But it is precisely this 

 which, as far as we know, remains in need of demonstration. Books, indeed, con- 

 tain scarcely anything tangible on the subject. One writer estimates the age of 

 an oak tree, 47 feet in circumference, to be not less than 1500 years ; another 

 (Marsham, writing of the Bentley Oak) gives the same age to a tree only 34 feet 

 round; sufBeient proof that no real guide to age was known to those writers. 

 The late Prof. Zuccarini endeavoured to work out this problem (see Lindley's 

 Intr. to Botany, 1, 204), but without success ; for he found such enormous differ- 

 ences between the rate of growth of specimens of the same species of tree (Yews 

 and Scotch Firs, the subject of his examination), as to be driven to the conclusion 

 that the age and number of rings of a tree cannot be determined with any proba 

 bility from the diameter, except when trees have grown under exactly similar 



