ENGELMANN — REVISION OF THE GENUS PINUS, ETC, 163 



about 20 years, in Catalpa not more than 3 or 3 years. The 

 thickness of the sapwood in pines is usually 2-4 inches, and rarely 

 under i inch ; in P. ponderosa I have found it sometimes even 

 10 inches. 



The wood cells and especially those more compact ones of the 

 late summer growth, the outer part of the layers, are often 

 strongly impregnated with resin and thereby darker colored, yel- 

 lowish or brown, and become in thin sections semi-transparent; 

 this is much more the case in those of the section Pinaster than 

 of Strobus. The former have mostly heavier and harder wood 

 than the latter, though we find exceptions, such as P. contorta^ 

 which has soft wood similar to that of the white pine or spruce. 

 Spirally marked cells, such as abound in Pseudotsuga and in 

 Taxus^ have not been found in the pines. 



The i.HAVES, in the wider sense, are of seven different forms: 

 the cotyledonous or seed-leaves, the primary leaves, the ordinary 

 bracts, the secondary leaves, the bracts constituting the sheath 

 of these, the bracts forming the involucrum of the male flowers, 

 and the bracts supporting the carpellary scale. 



The COTYLEDONOUS LEAVES form a whorl of 4 to 18 in num- 

 ber, are triangular, flat on the back, keeled above, higher than 

 broad and mostly entire ; in P. Strobus I find the keel slightly 

 spinulose -dentate. Stomata are found only on the inner and 

 upper sides, as is the case in the cotyledonous leaves of most 

 conifers ; those of Sciadopitys are, as far as I know, the only 

 ones that have stomata merely on the under and none on the 

 upper side. 



The PRIMARY LEAVES succeed the cotyledons on the main 

 axis ; in some species (P. inops^ P. rigida^ P. Canariensis^ etc.) 

 they ai-e also found on the sprouts. They are always subulate 

 from a broader base, flat, keeled on both surfaces, always serru- 

 late, even in those species whose secondary leaves are entire {^P. 

 eduiis)., with stomata in rows on both surfaces, more on the lower 

 than on the upper face. 



The primary leaves not rarely produce in their axils buds with 

 secondary leaves, but they are most generally reduced to bracts 

 {Hochblaetter) before their axils become productive. These 

 bracts are triangular-lanceolate, membranaceous or coriaceous, 



