i8 



THE PINES <>!' MEXICO. 



10. PINUS LAWSONI Roezl. 



Pinus Lawsoni Roezl, ex Gordon Pinctum, Appx, 64 (1862). Hemsley, Jiot. Biol. Cent. 



Am. iii, 187 (1883). 

 Pinus Altamirani Shaw, Sargent Trees & Shrubs i, 209, t. 99 ( 10P5). 



Leaves with persistent sheaths, in fascicles of 3, often of 4 or 5, not exceeding 24 cm. in 

 length, serrate ; resin ducts mostly internal, those in the angles of the leaf often medial ; outer 

 walls of endoderm cells not thickened, the 2 fibro-vascular bundles contiguous. Conelets on 

 retlexed peduncles, subterminal, rarely also lateral, single or in pairs, their lustrous brown 

 scales armed with a small prickle. Cones variable in size, usually 5-6 rarely exceeding 7 cm. 

 in length, unsymmetrical, rarely symmetrical, reflexed on a pliant peduncle, ovate or elongate- 

 conical, opening at maturity, deciduous, their apophyses usually dull yellowish brown, un- 

 equally developed, sometimes protuberant on some of the scales ; umbo large, often salient and 

 very conspicuous, its epiderm deciduous. Branchlets covered with a conspicuous white bloom, 

 the decurrent bases of the bracts deciduous. Cortex at first thin, deciduous and red, soon 

 becoming dark and more persistent. 



A tree 2025 m. high with glaucous-green foliage, growing only at subtropical levels and 

 associated with P. Pringlei and P. oocarpa. The geographical range of the species is not yet 

 accurately determined, but it is apparently confined to the southern and central western States. 



Nelson, 1760 (398563) Reyes, Oaxaca; 21S1 (39S569) Chilpancingo, Guerrero ; 2537 (3985S1), 2538 

 (39S5S2), 2540.(398584) Miahuatlan, Oaxaca. Pose & Hough, 4639 (346620) Las Sedas, Oaxaca. Pringle, 

 10017, Uruapan, Michoacan. Shaw, Uruapan, Jesus del Monte & Huingo, Michoacan ; Cuernavaca, Morelos ; 

 Las Sedas, Oaxaca. 



Among the Pines, with which it is associated P. Lawsoni is conspicuous by its glaucous foliage. Its de- 

 ciduous cone with its pliant peduncle cannot be confused with the persistent cone of P. Pringlei. In herba- 

 rium specimens normal cones are easily recognized, but an occasional cone may be found which resembles 

 that of P. teocote var. macrocarpa. The scales of the latter are, however, usually smaller and more numerous. 

 The resin-ducts of the leaf of P. Lawsoni are. usually internal, while those of P. teocote and its variety are usually 

 medial, but this character is not wholly reliable. I have so far found that the endoderm cells of the leaves of 

 P. teocote show thickened outer walls, while in those of P. Lawsoni there is no perceptible difference between 

 the outer and inner walls of the endoderm. In the localities where I have met them P. teocote and its variety 

 macrocarpa grow at higher levels and are never associated with P. Lawsoni. 



There are misleading statements in Gordon's description. The leaves are never entire, nor does the species 

 grow on the higher mountains of Mexico. The resemblance of its cone to that of P. sylvestris L. is of a kind 

 that diminishes with a better knowledge of the two species. 



PLATE XI. 



Fig. 1, 2, 3, 4. Cones from Huingo. 

 " 5. Cone of Nelson 2538. 

 " 6. Cone from Uruapan. 

 " S. Cone from the Kew Herbarium. 



Fig. S. Leaf-section, magn. 30 diam. 



" 9. Cone and conelets from Uruapan. 



" 10. Conelet, magnified. 



" 11. Leaf-section from Uruapan, magn. 30 diam. 



