; resin-ducts external. Pits of the ray-cells small.

The wood of this subsection differs from that of other species, except
that of P. pinea, in the Picea-like characters of the medullary
rays--tracheids with smooth walls combined with the thick walls and
small pits of the ray-cells. On the character of the seeds the species
may be divided into three groups.

Seeds wingless IV. Cembroides.
Seeds with a short, ineffective, articulate wing V. Gerardianae.
Seeds with a long and effective wing VI. Balfourianae.

=IV. CEMBROIDES=

Seeds wingless, the nut large, wholly or partly bare of membranous
cover. Cones varying from yellow-ochre to deep red-orange in color.

These are the Nut Pines, growing on the arid slopes and table-lands
above the great plateau of northern Mexico and its extension into the
southwestern United States. There are three distinct species.

Leaves entire, the sheath deciduous.
Cones subglobose, subsessile 13. cembroides.
Cones cylindrical, pedunculate 14. Pinceana.
Leaves serrulate, the sheath persistent 15. Nelsonii.

13. PINUS CEMBROIDES

1832 P. cembroides Zuccarini in Abh. Akad. Muench. i. 392.
1838 P. Llaveana Schiede in Linnaea, xii. 488.
1845 P. monophylla Torrey in Fremont's Rep. 319, t. 4.
1847 P. Fremontiana Endlicher, Syn. Conif. 183.
1848 P. edulis Engelmann in Wislizenus, Tour. Mex. 88.
1848 P. osteosperma Engelmann in Wislizenus, Tour. Mex. 89.
1862 P. Parryana Engelmann in Am. Jour. Sci. ser. 2, xxxiv. 332
(not Gordon).
1897 P. quadrifolia Sudworth, Bull. 14, U. S. Dep. Agric. 17.
1903 Caryopitys edulus Small, Fl. Southeast. U. S. 29.

Spring-shoots pruinose. Leaves from 2 to 6 cm. long, in fascicles of 1
to 5, the sheath-scales revolute at the apex, then deciduous; stomata
ventral, or ventral and dorsal; resin-ducts external. Scales of the
conelet armed with a minute prickle. Cones from 4 to 6 cm. long,
subglobose, subsessile; apophyses lustrous ochre-yellow, crowned with a
quadrilateral umbo bearing the minute prickle of the conelet; seed
flaxen yellow when fresh, its testa bare, the spermoderm adnate to the
cone-scale.

A broad tree with a round head, similar in size and form, but not in
ramification, to the cultivated Apple-tree; growing on arid slopes and
table-lands. Its east