306 PINUS. 



SUB-TEIBE III. SAPINE^E. 



Leaves persistent, for the most part homomorphic and inserted on 



cortical outgrowths or pulvini decurrent from their base. Fruit cones 

 maturing in one year. 



Leaves sessile or very shortly petiolate, angulate or 

 flat with one two lateral resin canals. Cones 



often large and pendulous ; scales persistent - 18. Picea. 



Leaves petiolate, flat, with a central resin canal. 



Gones small and pendulous ; scales persistent 19. Tsuga. 



Leaves flat with two lateral resin canals. Staminate 

 flowers solitary or umbellate. Cones pendulous 



(or erect), scales persistent - 20. Abietia. 



Leaves flat, rarely angulate, with two lateral resin 



canals. Cones large and erect; scales deciduous- 21. Abies. 



PINUS. 



Linnteus, Sp. Plant. II. 1000, in part (1753). Lambert, Genus Finns, I. in part (1803). 

 Endlicher, Synops. Conif. 81, in part (1847). Parlatore, D. C. Prodr. XVI. 377, in part (1868). 

 Bentham and Hooker, Gen. Plant. III. 438 (1881). Eichler in Engler and Prantl, Nat. Pfl. 

 Fam. 70 (1887). Masters in Joiirn. Linn. Soc. XXX. 37 (1893). 



The foliage of the Pines is so distinct from that of every other 

 genus of trees that the circumscription of Pinus is one of the 

 simplest ; as Dr. Engelmann remarked long ago, " nobody fails to 

 recognise the species belonging to it." This distinctness is owing 

 to the peculiar mode of production of the foliage leaves ; they are 

 not primary leaves in the ordinary acceptation of the term, but 

 secondary leaves borne on an undeveloped branchlet surrounded at 

 the base by bud-scales which form the "basal sheath."* Besides 

 this distinct form of foliation, there is an homogeneity of structure in 

 the reproductive organs of all the species, so that both floral and 

 vegetative characters unite to establish the genus firmly. 



The Pines are trees, often of large size ; shrubs only under the 

 severe climatic conditions of high altitudes and high latitudes. In 

 warm and even in temperate climates the larger Pines grow rapidly 

 for the first thirty to fifty years, and during that period the 

 proportion of sapwood to heartwood is greater than in any other 

 coniferous trees, and it is often strongly impregnated with resin. At 

 and near the extreme vertical limit the growth of the alpine species 

 is extremely slow throughout life ; and even when transplanted in 

 lower altitudes, with a higher annual temperature, their growth is 

 not only not accelerated but they soon perish under its stimulus. 



* See page 24 ; also Engelmann, Revision of the Genns Pinus in Transactions of the 

 Academy of Science of St. Louis, U.S.A. IV. 4 ; and Masters in Journal of the Linnean 

 Society, XXVII. 267, 



