14 BULLETIN 460, U. S. DEPARTMENT OF AGRICULTURE. 



Mature cones are from. 4f to 9^ inches long (Pis. VII and IX). 

 The most distinctive characteristic of the cone is the strongly renexed 

 thin tips of the cone scales. (PL VII, a, b.) No other pine in the 

 United' States has cones so strongly marked. The pendent cones are 

 mature about the middle of September and usually drop their seeds 

 by the middle of October. They fall from the trees in late autumn 

 or early winter. At maturity the cones are light yellowish-brown, 

 unexposed parts of the scales being dull red. The nutlike seeds are 

 dark brown, slightly tinged with red, a-nd are provided with a very 

 short wing. (PL VII, c, d.) The seed-leaves are from 10 to 12 in 

 number. (PL IX, a.) 



The wood of Mexican white pine is moderately heavy for a white 

 pine, a cubic foot of it when dry weighing about 30^ pounds. It is 

 rather hard and narrow-ringed ("fine-grained'' 1 ). The sap wood is 

 thin and whitish, the heartwoocl being a very pale reddish-brown. 

 In general appearance and texture lumber from this tree resembles 

 that from old trees of the eastern white pine (Pinus strobus), while 

 its " working " qualities are similar to those of western white pine 

 (Pinus monticola). The limited distribution of this tree in the 

 United States and its occurrence in places difficult of access has so 

 far prevented any but local use of the timber, the best grades of 

 which would readily serve as a substitute for western white pine. 



OCCrRKEXCE AXD HABITS. 



Mexican white pine grows in dry, rocky, or gravelly soils on moun- 

 tain slopes, canyon sides, and ridges at elevations of from about 

 5,500 to 9,700 feet; it is only very occasionally that straggling trees 



1 The popular conception of the " grain " of wood appears to refer mainly, if not en- 

 tirely, to the thickness of the annual layers of growth. Thus woods with thin or thick 

 layers of growth are commonly called " fine-grained " or " coarse-grained." Such other 

 qualities of wood as compactness or density and porosity of structure are popularly de- 

 scribed as " dense," " very dense," " compact," or as " porous " and " nonporous." In 

 view of this evident popular confusion in reference to " grain," it is here maintained that 

 grain should properly refer only to the structural constitution of wood within the annual 

 or other periodic layers of growth, and not to the thickness of the annual increment, 

 which is consistently described by such terms as " wide-ringed " and " narrow-ringed " 

 wood. Uniform thickness of the periodic layer of growth is only exceptionally character- 

 istic of any wood under all conditions of the tree's life, while the structural elements of 

 different woods remain fairly constant. The characteristic structure of different woods 

 results from the association of different individual cell-elements (fibers and vessels i. 

 These elements have distinctive forms, which vary within limits characteristic of dif- 

 ferent groups of woods, and also of the same species grown under different conditions. 

 Wood elements are also characteristically assembled in different genera and species of 

 woods. In one, these elements may be so associated as to form the popular and correctly 

 termed "cross-grained" wood, as in sycamore (Platanus) and in gum (Nyssa), etc. 

 In another, they may form " straight-grained " wood, as in white ash, white pine, etc. 

 Again, the elements may take a wavy longitudinal course, or an abruptly-curved course. 

 and produce the "curly-grained" and "birds-eye" wood. So also, when the elements 

 are spirally disposed with reference to the axis of the tree, the wood has a "twisted 

 grain." If all of the elements of a wood are small and about the same width, the struc- 

 ture can properly be termed " fine-grained." So, too, if many of the cell-elements are 

 large, the wood, produced is " coarse-grained." 



