226 JOURNAL OF THE ARNOLD ARBORETUM [vol. v 



Cones of lower phyllotaxis. 

 Ray-tracheids with smooth walls. 

 Bark-formation late. 



Diploxylon 



Fibro- vascular bundles of the leaves double. 

 Sheath of the leaf-fascicle persistent. 



Bracts subtending the leaf-fascicles decurrent on the branchlet. 

 Staminate flowers sufficiently developed in the winter-bud to be recog- 

 nized. 

 Connective of the pollen-sacs relatively large. 



Cones of higher phyllotaxis. 

 Ray-tracheids with dentate walls. 

 Bark-formation early. 



Several of these characters are subject to a few exceptions such as, for 

 instance, the persistent sheath of the Soft Pine, P. Nelsonii Shaw or the 

 deciduous sheath of the Hard Pine, P. leiophylla, the large connective of 

 P. excelsa Wall, or the small connective of P. sylvestris L., the late bark- 

 formation of P. halepensis Mill., P. psendostrobus Lindl., etc., etc. Never- 

 theless there is no difficulty in placing a species in its proper section, for, 



in every case, the determinative characters so predominate that the 

 recognition of a Soft, or a Hard Pine is immediate. 



SUBSECTIONS AND GROUPS 



In the section Haploxylon the subsections are determined by the 

 peculiarities of the cones while the groups follow the construction of the 

 seeds (Shaw, Gen. Pinus, 25, [1914]). In Flexiles, however, the seed is 

 not sufficiently distinct to justify the retention of this group. The seed- 

 wing, though very short, is nevertheless obvious and, like the wing of the 

 Strobi, is adnate to the nut. The seed-wings of the subsection Strobi vary 

 much in length and, in the P. ayacahuite Ehrenb., the wing of the northern 

 variety is almost rudimentary and so like that of P.flexilis James that the 

 demarcation between Flexiles and Strobi is not clearly defined. With 

 this change the subsections and groups should be tabulated as follows: 



A— HAPLOXYLON. 



a — Cemhha. 



Scales of the conelet unarmed, umbo of the cone-scales terminal, 



pits of the ray-cells large. 



I — Cembrae. 



Cones indehiscent. 



Seeds wingless. 



II — Strobi. 



Cones dehiscent. 



Seeds with an adnate wing. 



b — Paracemhka. 



Scales of the conelet armed, umbo of the cone-scales dorsal, 



pits of the ray -cells small. 



Ill — Cembroides. 



Seeds wingless. 



