562 THE POPULAR SCIENCE MONTHLY 



and have a sufficient underground supply of moisture. In the matter 

 of soil requirements, therefore, it is easily suited, and it is hardly neces- 

 sary to add that this is a distinct assei on the side of the perpetuation of 

 the species. 



Just as is the case with other organisms in both plant and animal 

 kingdoms, all our tree species possess an average age limit. Some of 

 the individuals of the species live longer, and others die out before the 

 limit is attained, but to every species one might assign an average length 

 of life. This aire limit differs, of course, with different species: for ex- 

 ample, some of the oaks are notably longer lived than such species as the 

 aspen or the gray birch. Sonic <>{ the causes of these differences in 

 longevity are obscure, and this is not the place for their discussion. 

 What we wish to point out is that trees as well as animals, vary in their 

 age limits. 



Now, a tree, on reaching maturity, begins to reproduce, that is it 

 forms seeds, which, if they find conditions suitable for them, develop into 

 individuals like their parent. I have here in my yard a silver maple, the 

 seed of which I planted in 1904. Two years ago, in 1912, when it was 

 eight years old, and about ten feet high, it bore a few blossoms and 

 seeds. Last year more seeds were produced than the year before, and 

 this year it is loaded with blossoms. Although still a small tree, not yet 

 ten years old, it is arriving at maturity, and is able to reproduce itself. 

 It should continue to do this until the end of its life. Of course under 

 modern city conditions, where, among oilier disturbing elements, the 

 ubiquitous lawn mower can always be counted on to do its deadly work, 

 it is a question how many, if any, of its descendants will survive. But, 

 nevertheless, here or anywhere, the chances of reproducing its kind de- 

 pend ultimately on the number of seeds it bears, and this number, again, 

 depends directly on the length of its life. 



It is clear then that with two species with differing age limits, other 

 things being equal, the species which is longer lived would have the 

 better chance to perpetuate its kind. 



When we consider the genu- Castanea, we find it especially favored 

 in this respect, for it has long been noted for its longevity. The follow- 

 ing extract from Sargent'? 17 " Silva of North America '" is of interest in 

 this connection : 



The Tortworth chestnut, tree on the estate of the Earl of Dueie, in Glou- 

 cestershire, which is still in a healthy condition, was remarkable for its great 

 size in the r^eign of Stephen, who ascended the English throne in 1135, and is 

 probably considerably more than a thousand years old. In 1776, the short trunk 

 of this remarkable tree measured fifty feet in circumference at fiye feet from 

 the ground. 



Further on. writing of trees on Mt. iEtna, in Sicily. Sargent says : 

 " Sargent. C. S.. loc. tit., 9: 8, 1896. 



