STEMS OF CONIFEROUS PLANTS. 11 



The power of forming roots by pieces detached from the parent plant, 

 or by "cuttings," is very considerable, but differs much in the different 

 tribes. It appears to exist nearly in the same ratio as that of producing 

 leaf buds j thus in the Cypress tribe, in which the branchlets ramify 

 repeatedly and produce lateral shoots very freely when the leaders are, 

 in garden phraseology, "headed back," cuttings take root very readily 

 when placed in circumstances favourable for their development. In the 

 Sequoia and Yew tribes the power of rooting from cuttings is almost as 

 great as in the Cypress and its allies. It is much weaker in the Fir 

 and Pine tribe ; some of the Araucarias possess it in a high degree ; 

 the Spruce and Hemlock Firs less so ; it is feeble in the Silver Firs, 

 and wanting, or nearly so, altogether in the true Pines. 



Stems. — The Stems of Coniferous plants, the internal structure of 



which we have just described, are Exogenous and ligneous or woody 



in texture j they attain generally a timber-like size, and consist of a 



heart-wood, the older growth, which in many species is very 



durable, and affords valuable wood for economic purposes; and a 



sap-wood, the later growth, which soon decays on exposure to the 



weather; the whole being enclosed in a tegument or bark similar 



in structure in all its essential parts to that of other Exogenous 



trees, but showing in some of the species some peculiarities. With 



very few exceptions the stems or trunks of Coniferous trees are 



cylindrical and tapering, growing perfectly erect, and attaining 



dimensions varying from a few inches* to upwards of 300 feet 



in height,f ail d vnth. diameters generally small in proportion to 



the height, but in this respect the Tew, the Cedar of Lebanon, and 



the deciduous Cypress are well known exceptions. The size attained 



by stems of the same species is far from being uniform except under 



like conditions, the growth being greatly influenced by soil, situation, 



or climate, or by a combination of these causes. Some species of 



Pinus and Abies, for example, having the slopes of mountains for 



their habitat, near the base grow from 60 to 100 feet high, or even 



more; but this height is found to diminish in proportion to the 



elevation at which they grow, so that at the highest point, often at 



the limits of perpetual snow, they are dwarfed to a more scrubby 



bush over which a man may step. A similar change is observed in 



species whose habitat extends over many degrees of latitude; thus, 



the Cembra Pine on the Swiss Alps, and under cultivation in our 



* Jwiiperus ommrmnia compressa, native of the Pyrenees, 

 t WeUinglonia gigcmtea, the Mammoth tree of California. 



