108, U.S.Forest Service: Tests of structural timbers, p.

37.] Rings per inch Douglas fir 24 Shortleaf pine 12 Loblolly pine 6 Western larch 18 Western hemlock 14 Tamarack 20 Norway pine 18 Redwood 30 No satisfactory explanation can as yet be given for the real causes underlying the formation of early and late wood.

Several factors may be involved.

In conifers, at least, rate of growth alone does not determine the proportion of the two portions of the ring, for in some cases the wood of slow growth is very hard and heavy, while in others the opposite is true.

The quality of the site where the tree grows undoubtedly affects the character of the wood formed, though it is not possible to formulate a rule governing it.