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THE AMERICAN NATURALIST [Vol. XLIV 



Asia, although belonging to the soft pine series have the 

 thick cone-scales and median dorsal umbo of the hard 

 pines. Nor is the nut-like character of the seed a con- 

 stant character, for the nut-pine of Italy is a hard pine, 

 while those of America and Asia are soft pines. If we 

 seek for really dependable criteria for the classification 

 of pines, we have to go below the surface. The single 

 leaf -trace, for example, is absolutely constant throughout 

 the soft-pine series as is equally the case with the double 

 foliar bundle in the hard-pine series. Similarly, the 

 soft pines are characterized by a single row of resin- 

 canals in the first year's growth which is duplicated or 

 further multiplied in the hard pines. Englemann has 

 further indicated the value of the number and position 

 of the resin canals in the leaf for diagnostic purposes. 

 An extremely important anatomical character for the 

 separation of the two great series of living pines is the 

 nature of the tracheid-like cells on the margins of the 

 wood-rays. The nature of the pitting in the tracheids 

 of the wood and the central cells of the wood-rays like- 

 wise supply valuable criteria for the establishment of 

 smaller subdivisions. It will be inferred from what has 

 been said, that anatomical characteristics in the case of 

 Pinus are very constant in broad lines and consequently 

 are for the establishment of a natural classification, in- 

 dicating the evolution of the genus, of the greatest 

 value. External characters, on the other hand, are 

 much subject to variability. 



Two main series of pines, the hard pines and the soft 

 pines, may be clearly recognized, in accordance with ana- 

 tomical characters. For example, the groups of which 

 P. strobus Linn, and P. silvestris Linn, are types, are 

 quite distinct. The latter species is characterized with 

 the remaining hard pines, without exception, by the 

 double foliar "fibre-vascular bundle, two or more rows of 

 resin canals in the first ring of woody growth and den- 

 tate or reticulate marginal tracheids of the wood-rays. 

 The former species, together with the other soft pines, 



