262 BOTANY. 



parts of that district and generally known there as "yellow pine". A most 

 variable tree, several forms of which have received distinct, specific appel- 

 lations, but the specimens collected in these expeditions all appear to 

 belong to the ordinary smaller-leaved and smaller-fruited form. Whenever 

 the macroscopic characters leave any doubt, the microscopic structure of 

 the leaf appears to offer a sure guide. The leaves contain two or three or 

 often more parenchymatous resin-ducts, usually of uncommonly small diame- 

 ter, always with some, and often surrounded by many, of those strengthening 

 cells of which I have spoken before; the same cells occur within the sheath, 

 above and below the bundles of vessels. I have examined the leaves of 

 20-30 specimens from the whole range of the species, and have never failed 

 to discover this same structure, which I must therefore consider as char- 

 acteristic of the species. 



Pinus Chihuahuana, Engelm. in Wislizen. Mem. note 26 ; Parlat. I. c. 

 397. — A middle-sized tree, with ternate, closely serrulate leaves 2 £-4' 

 long; the loose glistening sheaths £' long, deciduous after the first season; 

 stJtminate flowers slender, cylindric, about £' long, sometimes interspersed 

 among the foliage; involucre as long as the nearly entire-margined bract, 

 of 8-10 scales, the outer about half as long as the inner ones ; anthers with 

 an almost orbicular crest ; oval cones sub-terminal, small, 1^' long ; knobs 

 of the scales bearing recurved, deciduous prickles. 



Southern Arizona, in Sanoita Valley, at 6,500 feet altitude, -Rothrock 

 (649), in 1874 ; also Wright, and in Western Chihuahua, Wislizenus. — A 

 tree 30-50° high, " with bark resembling yellow pine "; easily distinguished 

 by the characters given, and especially by its deciduous sheaths. All the 

 Strobi and Cembroids have such deciduous sheaths, but among the Pinas- 

 ters the sheaths are persistent, except in one or two Mexican species, in P. 

 Bungeana, above mentioned, and in this species. Leaves strongly and 

 closely serrulate, and with three or often four parenchymatous ducts. 



Pinus contorta, Dough, var latifolia, Engelm.; P. Murrayana, Balf. 

 Oreg. Com. Rep. — A middle-sized tree, sometimes 60-80° high, and 2-4° 

 in diameter, with thin, scaly bark of grayish to red-brown color, and close, 

 white, rather soft wood; leaves in pairs, 1^—2' or rarely 3' long and 1" 

 wide ; staminate flowers oblong, 6" in length, their involucre commonly of 



