GENUS PINUS 17 



In both sections of the genus are found the effective adnate wing (Strobi and Longifoliae) and the 

 inefficient articulate wing (Gerardianae and Pineae). A Httle examination of all forms of the seed 

 will show that they blend gradually one into another. 



The color of the wing is occasionally peculiar, as in the group Longifoliae. There is usually no con- 

 stancy in this character, for the wing may be uniform in color or variously striated in seeds of the same 

 species. The length and breadth of the seed-wing, being dependent on the varying sizes of the 

 cone-scale, differ in the same cone. They are also inconstant in different cones of the same species, 

 and of this inconstancy the seed of P. ayacahuite furnishes the most notable example. 



THE WOOD. Plate VII. 



With the exception of the medullary rays, a very small proportion of the whole, the wood of Pinus, 

 as seen in cross-section (fig. 82), is a homogeneous tissue of wood-tracheids with interspersed resin- 

 ducts. In tangential section the medullary rays appear in two forms, linear, without a resin-duct, 

 and fusiform, with a central resin-duct. In radial section the cells of the linear rays are of two kinds, 

 ray-tracheids, forming the upper and lower limits of the ray, characterized by small bordered pits, 

 and ray-cells, between the tracheids, characterized by simple pits. 



The walls of the ray-tracheids may be smooth or dentate; the pits of the ray-cells may be large or 

 small. These conditions admit of four combinations, all of which appear in the medullary rays of 

 Pinus, and of which a schematic representation is given in Plate VII. These combinations are 



Ray-tracheids with smooth walls. Soft Pines. 



Ray-cells with large pits Subsection Cembra fig. 80. 



Ray-cells with small pits Subsection Paracembra fig. 81. 



Ray-tracheids with dentate walls. Hard Pines. 



Ray-cells with large pits Group Lariciones fig. 83. 



Ray-cells with small pits Other Hard Pines fig. 84. 



This, the simplest classification of Pine-wood, is not without exceptions. P. pinea of the Hard Pines 

 resembles, in its wood-characters, P. Gerardiana and P. Bungeana of the Soft Pines. The dentate 

 ray-tracheids of P. longifolia are not always obvious. The tracheids of P. luchuensis, according to 

 Bergerstein (Wiesner Festschr. 112), have smooth walls. My specimen shows dentate tracheids. 

 There is also evidence of transition from small to large pits (I. W. Bailey in Am. Nat. xliv. 292). 

 Both large and small pits appear in my specimen of P. Merkusii. 



Of other wood-characters, the presence or absence of tangential pits in the tracheids of the late wood 

 establishes a distinction between Soft and Hard Pines. These pits, however, while always present 

 in Soft Pines, are not always absent in Hard Pines. The single and multiple rows of resin-ducts in 

 the wood of the first year may prove to be a reliable sectional distinction, but this character has not 

 been sufficiently investigated to test its constancy. The wood-characters, therefore, however deci- 

 sive they may be for establishing the phylogenetic relations of different genera, must be employed 

 in the classification of the Pines with the same reservations that apply to external characters. 



Ray-tracheids with dentate walls and ray-cells with large pits are peculiar to Pinus. Therefore the 

 presence of these characters, alone or in combination, is sufficient evidence for the recognition of Pine- 

 wood. But the combination of smooth tracheids with small pits (subsection Paracembra) Pinus 

 shares with Picea, Larix and Pseudotsuga. 



Among Hard Pines the size of the pits has a certain geographical significance. The large pits 

 are found in all species of the Old World except P. halepensis and P. pinaster; the small pits in all 

 species of the New World except P. resinosa and P. tropicalis. The Asiatic P. Merkusii with both 

 large and small pits is not strictly an exception to this geographical distinctiion. The four excep- 

 tional species by this and by other characters unite the Hard Pines of the two hemispheres. 



