EFFECT OF AGE. 



17 



Logs from the top cau usually be roeosiiizod by the hiiger pereeiitage of sapwood and the 

 sinaller i)rop()itioii and more regular outlines of the bands of sumnierwood, which are more or less 

 wavy in the butt k)gs. 



Both weight and streugth vary in the different 

 parts of the same eross section from eeuter to periph- 

 ery, aud though the variations appear frequently 

 irregular in single individuals, a detinite law of rela- 

 tion is nevertheless discernible in large averages, and 

 once detern)ined is readily observable in every tree. 



A separate inquiry, avoiding the many variables 

 which enter into the mechanical tests, permits the fol- 

 lowing deductions for the wood of these pines, and 

 especially for Longleaf; the data I'eferriiig to weight, 

 but by inference also to strength : 



1. The \ariation is greatest in the butt log (the 

 heaviest part) and least in the top logs. 



•2. The variation in weight, hence also in strength, 

 from center to periphery depends on the rate of 

 growth, the heavier, stronger wood being formed dur- 

 ing the period of most rapid growth, lighter and 

 weaker wood in old age. 



3. Aberrations from the normal growth, due to 

 unusual seasons aud other disturbing causes, cloud 

 the uniformity of the law of variation, thus occasion- 

 ally leading to tlie foiiuation of heavier, broad ringed '"^^' 

 wood in old, and lighter narrow-ringed wood in young- 

 trees. 



4. Slow-growing trees (witli narrow rings) do not 

 make less heavy, nor heavier wood than thriftily 

 grown trees (with wide rings) of the same age. (See 

 tig. 2.) 



EFFECT OF AGE. 



The interior of the butt log, representing the 

 young sapling of less than fifteen or twenty years of 

 age, and the central portion of all logs containing 

 the pith and two to live rings adjoining, is always 

 light and weak. 



The heaviest wood in Longleaf and Cuban Pine is 

 formed between the ages of fifteen and one hundred 

 and twenty years, with a specific weight of over 0.(50 

 and a maxinuim of 0.G6 to 0.08, between the ages of 

 forty and sixty years. The wood formed at the age 

 of about one hundred years will have a specific 

 weight of 0.62 to 0.03, which is also the average 

 weight for the entire wood of old trees; the wood 

 formed after this age is lighter but does not fall below 

 O.oO ui) to tlie two hundredth year; the strength 

 varies in the same ratio. 



In the shorter-lived Loblolly and Shortleaf the 

 period for the formation of the heaviest wood is 

 between the ages of fifteen and eighty, tiie average weight being tlieu over 0.50, with a maximum 

 of O.o7 at the age of thirty to forty. The average weight for old trees (0.51 to 0.52) lies about 

 the seventy-flfth year, the weight then falling off to about 0.45 at the age of one hundred and 

 forty, and continuing to decrease to below 0.38, as the trees grow older. 

 17433— No. 13 2 



tr^iyi 



BOO 



Sc/ti£ i^£ffr/CAi /s M. = //vr 



Fig. 2. — Schematic section through stem of Lon;:ie:if Piue, 

 sliowiug variation of specific weiglit witli lieiylit, iliamctcr, 

 and age at twenty (a/^fi), sixty (t/ct/), one huiulrcd ami twenty 

 {eeee), and two liundrod (/^//) years. 



