THE PINES OF MEXICO. 



I I 



PlSTUS AYACAHUITE VAR. BRACHYPTERA N. VAR. 



Pinus strobiformis Engelmann, Wislizenus Tour Nor. Mex. 102 {Senate Doc. 1848). 



Differing from the species by its short ineffective seed-wing and large nut. 

 Northern States of Mexico. 



Nelson 4555 (398618) El Salto, Durango; 4915 (No Museumji umber) Mt. Mohinora, Chihuahua; 6043 

 (398625) Sierra Madre, Chihuahua. Shaw, Sandia, Durango. 



By the courtesy of Dr. Trelease, Wislizenus' specimen from which Engelmann established the species P. strobi- 

 formis was sent to the Arnold Arboretum for comparison with the cones of the Nelson collection and with other 

 material at hand. Wislizenus' cone is identical with that of Nelson 4915 and with one of my cones from northern 

 Durango. At the time when Engelmann wrote the Botanical Appendix to Wislizenus' Tour he was not acquainted 

 with Ehrenberg's species; in his Revision of the Genus Pinus (1880) Engelmann abandoned the name strobiformis. 



Reviewing the characters of P. ayacahuite, the number of leaves in the fascicle is almost invariably 5; exceptions 

 are very rare and, in my experience, confined to young trees; the difference in the hypoderm and in the number 

 of the resin ducts may be found in other species; these differences do not appear to be correlated with other char- 

 cters in a manner that can be utilized either for the separation of P. ayacahuite into two or more species or for 

 the determination of varietal forms. The same is true of the size and shape of the cones and the degree of 

 protuberance or curvature of their scales. 



The remarkable variations in the length of the seed-wing of P. ayacahuite are valuable for determining the 

 relative importance of this character. It is evident that the diagnostic value of the seed-wing must depend, not on 

 its dimensions, but on its construction. Eliminating the question of length there is no difference between the seed- 

 wings of P. ayacahuite, P. Lambertiana and P. ftexilis, therefore P.ftexilis is here associated with the White Pines 

 where Engelmann placed it, and the similarity of its cone-scales and its leaf-section to those of P. Lambertiana 

 confirms this conclusion. 



Fig. 1, 2. Cones from N. Durango. 

 " 3. Scale of cone 1. 

 " 4. Seed of cone 2. 



PLATE VI. 



Fig. 5- 

 " 6. 



Leaf-section, magn. 30 diam. 

 Leaf-section of Nelson 4555, magn. 30 diam. 

 7. Conelet. 



