WHITE FIXES OF WESTERN NORTH AMERICA 231 



from the Section Strobus by having a dorsal rather than a terminal cone 

 scale umbo. In the two Balfourianae species the umbo is armed with a sharp 

 prickle, and in several of the Cembroides species (P. Qerrbvoid.es Zucc. 

 and other pinyons, as well as P. pinceana Gord. and P. nelsonii Shaw), 

 as well as the new species, the umbo is armed but only bluntly so. Also 

 in the Balfourianae pines the seeds are definitely winged (as they are 

 in the new species), while the Cembroides pines are wingless. Unlike 

 the Section Strobus and Subsection Balfourianae, but like the Cembroides 

 pines, the new species has fewer (3 to 4) than 5 needles per fascicle. 

 I have suggested to Messrs. Madrigal and Caballero that the new species 

 might be a bridging species, and that attempts at crossing it with 

 Section Strobus and Subsection Balfourianae and Cembroides pines might 

 be profitable from the taxonomic standpoint. 3 



VAN' ARSDEL : I would like to suggest a slightly different interpre- 

 tation on the outliers of Pinus strobus L. in the U.S., and particularly 

 in the Mississippi River valley, than that suggested by Dr. Kriebel in 

 his excellent paper. Dr. Kriebel suggested that the outliers were 

 distributed according to microclimate. I'd like to suggest that the 

 distribution could also be related to edaphic conditions--! .e . , sandstone 

 outcrops. In the upper Mississippi basin (above Tennessee) the northern- 

 most outliers occur in Wisconsin on LaCrosse Sandstone, moving over into 

 Indiana they occur on St. Peters Sandstone, further south in Indiana they 

 occur on Manteyo Sandstone, and well to the south in Kentucky they occur 

 on another massive sandstone outcrop. The point is that on these sandy 

 outcrops there's no other tree competition. P. strobus occurs even on 

 the warm, southwest -facing slopes where it gets pretty hot, rather than 

 in cool, moist microclimates. 



KRIEBEL: I believe that in Ohio there is a climatic factor involved. 

 In that region we find Pinus strobus mainly restricted to stream valleys 

 and rather protected sites that are definitely cooler than surrounding 

 areas. However, I think what you say about edaphic (soil or geologic) 

 factors in the upper Mississippi Valley may be quite true. 



CALLAHAM: I have enjoyed this excellent geographic summary on the 

 white pines, but I hear repeated references to crossability . I'm 

 wondering if there is any intention to bring all of this evidence on 

 crossability together. It would complete the proceedings for these 

 panels if we could have some sort of crossability summary. 



BINGHAM: Earlier this morning when I could see this crossability, 

 and taxonomical questions arising, I asked Mr. Morton of my staff to 

 circulate a handout--on white pine taxonomy and crossability--prepared 

 for use with my own paper on taxonomy, crossability, and blister rust 

 resistance to be given later this afternoon (Bingham, these proceedings). 

 Apparently Mr. Morton was unable to complete the circulation due to the 

 starting of this afternoon's session, but he'll finish the job now. The 

 right, or last column of the handout on taxonomy, synonomy, botanical 

 range, and crossability of 5-needled white pines summarizes present 

 information on crossability amongst Subsection Cembrae, Strobi y and 

 Balfourianae white pines . 



3 Editors' note: Since this discussion it has come to our attention 

 that Madrigal and Caballero have already published their proposed new 

 species Pinus rzedowskii — see Madrigal, X. and M. Caballero. 1969. Una 

 nueva especie Mexicana de Pinus. Inst. Nac. due Invest. Forestales Mexico. 

 Bol. Teen. 26 } 12 p. 



