TORREYA 



January, 1915. 

 Vol. 15 No. I 



NOTES ON THE DETERMINATION OF ROCKY 

 MOUNTAIN CONIFERS 



By Seymour S. Sharp 



While working in a course in plant histology under the direction 

 of Professor Aven Nelson two years ago, I found that the different 

 species of the family Pinaceae occurring in the Central Rocky 

 Mountain region could readily be separated merely on the internal 

 structure of their leaves. Further study has led to the develop- 

 ment of this paper. 



In several instances, already, the key has proved of value in 

 determining incomplete specimens in the Rocky Mountain 

 Herbarium. Most of the species may be determined from a 

 cross-section of a leaf merely by a hand lens, especially after 

 one has become familiar with the terms used in the key and 

 their significance. Cross-sections of dried leaves may be easily 

 cut after boiling the leaves in water for a few minutes, and then 

 putting them into 50 per cent, alcohol. Extremely thin sections 

 are not at all necessary or advisable; in fact I have for my own 

 amusement made determinations in the field (where it was not 

 even necessary) with only a pocket knife and a hand lens. Not 

 much variation occurs in leaves from a given species, but to 

 avoid any possible confusion several leaves should be used. 

 Particularly should sections be cut from four or five places along 

 a leaf, so that typical sections may be secured. Since in some 

 leaves not all the ducts will extend the full length of the leaf, 

 this precaution becomes necessary. Fresh sections are sufficient 

 for determination, but sections stained and cleared are much 

 better. Fuchsin has been found to be a useful stain, since only 

 the gross structure is necessary. 



[No. 12, Vol. 14, of ToRREYA, comprising pp. 229-267, was issued 13 January 1915] 



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