The Black Spruce. 



291 



like successful tree growth on the tops of these mountains. 

 The two extremes of the black spruce have now been 

 noticed. The one a noble forest tree fifty to eighty feet 

 high with a well formed trunk one to two feet in diameter 

 at the base, supporting a symmetrical top or head of 

 branches covered with dark green leaves, the other a 

 dwarf of the mountain top scarcely a foot high, with no 

 distinct trunk and without strength to maintain an erect 

 position, its stunted branches spreading two ways and 

 bearing short, yellowish-green leaves, the whole looking 

 very much as if it were a feeble branchlet of the former 

 thrust obliquely in the ground. What thoughts do they 

 suggest concerning the variability of the species, what 

 concerning its stability. Surely a remarkable degree of 

 variation, a singular tenacity of life, a wonderful power of 

 adaptation to altered conditions is manifest. The spruce 

 shows itself capable of maintaining an existence under 

 most adverse circumstances. It grows where very few 

 other trees can grow. But at the same time it shows that 

 there is a limit to its variability, and that there are bounds 

 to its powers of adaptation beyond which it cannot pass. 

 The stately forest spruce can not stand on the summit of 

 Mt. Marcy but its wonderfully diminutive descendant may 

 maintain a feeble individual existence there. I say indi- 

 vidual existence for this dwarf does not appear to be capa- 

 ble of propagating itself by seed. And herein appear the 

 limits of its variability. When the reproductive power 

 fails the utmost degradation and variation of the species 

 seems to be reached for it can then only maintain an in- 

 dividual existence. This power is the great conservator 

 by which the integrity of species is preserved ; it is the 

 dead line beyond which if they go destruction awaits them. 

 Nature seldom fails to brand with sterility excessive de- 

 partures from her normal forms, no matter whence these 

 departures come, whether from starvation or stimulation, 

 self-fertilization, or hybridization. 



