600 EDITORIAL NOTES. [Feb. 



heartwood. It matters not whether the growth be rapid or slow, 

 heartwood must appear at or within a brief period of its arriving at 

 a certain age, varying only in point of time in proportion to tlio 

 difference of soil and climate as exerted on the individual during 

 its period of growth. In a colloquial sense, it may be admitted 

 there is a general foundation of accuracy in this connuonly re- 

 cognised opinion. No doubt the individuals of a species, such as 

 the larch, or any other grown in the same soil and other circum- 

 stances, on attaining a certain age will present relative proportions 

 of heartwood to sapwood sufficiently close to establish tlie general 

 conclusion. But this is merely stating in other words the fact that 

 it takes so many years to bring the individuals of a particular 

 species to maturity. What is really meant by tlie statement that 

 heartwood begins to form at a certain age in any tree is simply that 

 it has become visible, and presents a marketable quantity in relation 

 to the sapwood out of which it is formed. But this is a totally 

 different thing to what is implied by the statement, and also as to 

 what really takes place in the growth of a tree. The formation of 

 heartwood, like that of sapwood, begins with the birth of the tree. 

 The exercise of the functions leading to the building up of sap and 

 other vessels which form the structure of the newly-born plant, is 

 the point at which the formation of sapwood and heartwood alike 

 begin, and the processes go on concurrently season after season. 

 Not perhaps with invariable results in even the individuals of the 

 same species ; certainly not in all species alike. Some species are 

 slow to exhibit the same relative proportion of heartwood to sap- 

 wood that otliers do. And this may, as a general rule, be taken as 

 an index of the longevity of a species ; those, sucli as the oak, 

 which are slow in forming heartwood being longer-lived than most 

 of the species of conifers which form their heartwood more rapidly, 

 or in other words, arrive at maturity earlier. But the process of the 

 formation of heartwood goes on concurrently with that of sapwood 

 from the first development of the plant from the seed, whether 

 growth be slow or rapid, whether maturity be arrived at in a few 

 years or after many years. Briefly, the conversion of sapwood into 

 heartwood is accomplished by the thickening and indurating of the 

 walls of the sap vessels, and by the deposition in them of the 

 peculiar secretions of each species, such as gums, resins, etc., result- 

 ing from functional action, by which they eventually become filled 

 up, and their original use as channels for the upward flow of the 

 sap ceases. The time required to complete the process varies in 

 different species, and even in individuals of the same species, accord- 

 ing to circumstances already alluded to as affecting comparative 

 rapidity of growth. 



