CURRENT LITERATURE 



NOTES FOR STUDENTS 



Distribution of Pinus Banksiana and Thuja occidentalis. — In a recent 

 issue of this journal Hutchinson' has discussed the limiting factors controlling 

 the distribution of forest trees in northern Canada. Most of his points seem 

 to have been well taken, and his conclusions in accord with the observed facts. 

 He lays considerable emphasis on certain peculiarities in the distribution of 

 Pinus Banksiana and Thuja occidentalis. The latter he regards as having 

 migrated from a limited central area so slowly that it has not reached its 

 ecological Hmits; while the former has had its extent modified by competition, 

 which it seems less able to resist than severe conditions in its environment. 



More recently Fernald^ has offered another explanation for the irregu- 

 larities of these two trees, and has criticized Hutchinson's article in a decidedly 

 unsympathetic manner. He comments upon the accidental use of Abies 

 canadensis in the legend of a map when it is quite evident from the text that 

 Abies balsamea is intended (this correction was made by the author in the 

 errata published in the June number of the Botanical Gazette). He also 

 points out certain minor omissions and irregularities which somewhat modify 

 Hutchinson's limits of various species. His main point, however, is to offer 

 an entirely different explanation for the peculiarities in the range of the two trees 

 just mentioned. From data obtained chiefly from the reports of the Geological 

 Survey of Canada, he shows that Pinus Banksiana is found principally on 

 sands, acid rocks, and in acid swamps. This seems to support his contention 

 that the "Banksiana pine is a pronounced oxylophyte." The evidence 

 presented is such that it seems at least entirely probable that the Hmiting factor 

 in the distribution of this tree may be largely one of soil. This is rather 

 strengthened by the records of certain of its outposts in southeastern Minne- 

 sota^ upon sandy soil. It does not seem, however, that the fact that Pinus 

 Banksiana is to be regarded as a tree of acid habitats invalidates Hutchinson's 

 conclusion that it is limited in many parts of its range by competition. 



Fernald seems also to make a good case for Thuja being confined in its 

 best development and in many of its outlying stations to calcareous areas. 

 The failure of Thuja to reach Newfoundland would be due, as he contends, to 



' Box. Gaz. 66:465-493. 1919. 



^ Fernald, M. L., Lithological factors limiting the ranges of Finns Banksiana 

 zjid Thuja occidentalis. Rhodora 21:41-67. 1919. 



3R0SENDAHL, C. O., and Butters, F. K., On the occurrence of Pinus Bank- 

 siana in southeastern Minnesota. Plant World 21 : 107-113. 191 8. 



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