SOME NORTH AMERICAN CONIFERS 519 



NOTES ON SOME NORTH AMERICAN CONIFERS 

 BASED ON LEAF CHARACTERS. 



L. W. DURRELL. 



Leaf characters, unlike stem characters, are as a rule sub- 

 ject to such variations that they form an unreliable basis of 

 comparison between plants. Conifer leaves on the contrary, 

 because of their simplicity as compared with other leaves, show 

 a large degree of uniformity, particularly in those characters 

 seen in cross section. 



In preparing material for a class in dendrology it occurred to 

 the writer to make sections of conifer leaves to show these leaf 

 characters that they might be used, not wholly as a means of 

 identification in themselves, but to supplement other identify- 

 ing characters. Leaves of all the arboreal conifers of North 

 America bearing needle leaves (except Pinus) were examined and 

 the characters of the same species were found to be constant 

 even though the specimens come from widely separated locali- 

 ties. With this in mind camera-lucida drawings were made of 

 representative sections taken from the middle of mature leaves 

 from different points on the branch, and the drawings supple- 

 mented by a description of the section when treated with re- 

 agents to differentiate the histological elements. 



As the leaf characters of conifers have frequently been dis- 

 cussed and used in identification, the following drawings rather 

 than the keys or description are of most importance, as a means 

 of quick and vivid portrayal of these characters. The drawings 

 endeavor to show all the characters seen in cross section both as 

 a whole and in detail, except in the case of the stomata, which, 

 because of their alternate arrangement in their rows, do not 

 appear in the regular number in any one section. 



The scale of magnification for each plate is the same — the 

 drawing of the whole section in each case is enlarged to 40 

 diameters while the detailed drawings are enlarged to 260 di- 

 ameters, except in the case of Plates XL and LXVI, which are 

 reduced one-third more than the other plates. 



