Relation of Annual Rings to Age. 173 



TABLE COMPARING RINGS AND METEOROLOGY. 



The most exact results, such as I hope to obtain as soon as 

 another opportunity offers, would be secured by the use of a 

 plauinieter to determine the area of each separate ring of growth, 

 and from that its mean thickness. The circumstances of the case, 

 however, necessitated less exact methods. 



In the course of these examinations, it has been observed inci- 

 dentally that the rings of growth show a regularity of increase or 

 decrease in thickness which is quite independent of those varia- 

 tions previously referred to. In other words, the first formed layers 

 are thinnest or thickest, and those subsequently formed either 

 steadily increase or diminish in thickness with each succeeding 

 year, and thus there is produced what may be termed the curve 

 of accelerating or diminishing growth, which is quite independent 

 of the waves representing annual variations from other causes. 



Examining our specimens in this direction it was found that 

 of the eleven tropical woods forming distinct rings, the inner- 

 most rings were broadest in two cases, while in the remaining nine 

 there appeared to be uniformity of thickness throughout. An 

 examination of thhty-five native Canadian woods gave the follow- 

 ing :— 



1. Central rings broadest 10 



2. Outer rings broadest 11 



3. Cycles of increase and diminution 3 



4. Rings uniform throughout 11 



35 

 The first case, in which the rings steadily decrease in thickness 

 from the centre outward, is illustrated in Tsuga canadensis, 

 Betula nigra, Uhmisfulva, Fi^axinus sambuci folia, Amelanchur 

 canadensis, Primus americana, Rhus tyj)hina, Acer dasycarpum, 

 Zanthoxylum aimricanum, and Tilia americana. The second 

 case, in which the rings continually increase in thickness with 

 each year of growth, is illustrated in Picea nigra and alba, 

 Pinus resinosa and strobus, Thuya occidentalis, Abies balsamea, 

 Qvercus rubra, Corylus rostrata, Fagus ferruginea, and Pirus 

 americana. From what has been observed in other cases, it seems 

 highly probable that, had the specimens been of sufficient age, 

 this continued increase in thickness would have been succeeded 

 by as regular a diminution, thus bringing these eleven cases in 



