GROWTH IN THICKNESS. 



35 



The higher sections exhibit not only a regular course, but an entirely similar one, from cross 

 section to cross section. There is no reason to assume that the course at breast height would uot 

 follow the same law; therefore there can be constructed a curve for this height similar to the 

 curves of higher sections, using for guide points the data obtained from a series of measurements 

 made to establish the yield of pine in which trees were measured at breast height (compiled in 

 tables in the Appendix). This has been done on the diagram in the Appendix, which shows the 

 diameter development of different cross sections for dominant trees. From this can be read 

 the following average dimensions as approximating the diameters of each decade, leaving out 

 the uncertainjuvenile stage: 



Diameter, breast high, of White Pine (averages approximated), in inches. 



That these figures may be considerably exceeded (even by 50 to 60 per cent) under favorable 

 conditions will appear from the various tables of measurements in the Appendix. Especially is 

 this the case in the second-growth groves of pine. 



As will be readily seen in the curves after the juvenile stage, during which the diameter 

 grows very slowly, an acceleration in the rale takes place, which soon reaches a maximum, 

 continuing at that for a short time, and then slowly and persistently declining from about 3 inches 

 per decade between forty and fifty years to 1J inches at one hundred years, and half that amount 

 at two hundred years. 



DETAIL MEASUREMENTS OK ANNUAL GAIN IN CIRCUMFERENCE. 



An interesting set of most accurate observations have been made and reported by Mr. 

 Nathaniel Morton, of Plymouth, Mass., exhibiting 38 young trees of White Pine, which had 

 sprung up among oak and other hardwoods, mixed with White Pine and a few Pitch Pine in an 

 old, rather-neglected piece of woods, and which were measured every year from 1891 up to 1898. 

 The trees stand rather open. The age varied from twenty-eight to forty-two years, most trees 

 being between thirty and thirty-six years old and their average age thirty-six years in 1891. 



In 1891 the average cross section 3 feet from ground was 131 square inches; in 1898, 197 

 square inches ; the growth 66 square inches, or about 9 square inches per year, one tree making 

 15 square inches per year. This growth corresponds to a growth in circumference of about 1.3 

 inches per year, or a growth in diameter of four-tenths of an inch per year. 



The detail measurements are given in the following table : 



TABLE V. Annual gain in circumference of White Pine trees in Massachusetts. 



