164 TRANS. ST. LOUIS ACAD. SCIENCE. 



entire or mostly fringed on the edges, more or less persistent or 

 mostly deciduous, sometimes articulated above their base. 



The SECONDARY LEAVES constitute the foliage of the tree : 

 they are borne on an undeveloped branchlet in the axils of pri- 

 mary leaves or mostly of bracts, and are surrounded at base by a 

 sheath of bud-scales {Nieder blaetter). These consist of 2 shorty 

 rigid, strongly keeled, lateral bracts and a number (6-10 or more) 

 of longer, thinner inner ones, which generally are woven together 

 by the delicate fringes of their edges, and are then persistent with 

 the leaves, though in time worn oft' at the ends ; or they are loose, 

 at last spreading and deciduous at the end of the first season. 

 This is the case in all the species of the section Strobus^ \\\ the 

 nut-pines, and in a few others: /'. Balfouriana^ Gerardiana^ 

 Bu72geana^ Chihuahuana^ and usually also in P. leiophylla. 



The secondary leaves generally occur in definite numbers, i to 

 5, in a bunch, or their number is slightly variable : some species 

 have regularly 2 and 3 leaves {P. mitis, P. Elliottii)^ others 

 vary with 3 to 5 leaves {P. Mo7itezuince) ; species with regularly 3 

 leaves have occasionally 2 or 4, such with 5 leaves are sometimes 

 found with 6 and even 7 leaves. Where we have one (only in 

 P. monophyUd)^ the leaf is terete ; where there are two, the leaves 

 are semi-terete, convex on the lower surface and flat on the upper 

 one when fresh, or channelled when dry. Those leaves that 

 grow in bundles of 3 or more are triangular, the upper surface 

 being more or less elevated and keeled ; ternate leaves are gener- 

 ally somewhat flatter, and quinate ones higher and regularly 

 triangular. Thus the shape of the leaf and especially its trans- 

 verse section is mostly sufficient to determine the number in which 

 they occur. 



The leaves are in most species minutely but sharply serrulate 

 on the edges, and mostly also on the keel of the upper surface. 

 These serratures are closer together, or more distant, coarser or 

 more delicate, but are absent only in a very few West-American 

 species : the cembrotd or nut-pines, P. Balfouriana., and most 

 forms of P. Jiexilis. The tips of the leaves are generally entire, 

 acute, or acuminate, rarely obtusish ; but in all the species of the 

 section Strobus they are in the young and fresh leaves finely 

 denticulate. 



The stomata are usually distributed in longitudinal rows over 



