NOTES ON BARK STRUCTURE 



Theo. Krueger. 



There is very little material in English on the subject of 

 bark structure, and most of that is of a very general nature. 

 It was thought that the following notes would be useful especi- 

 ally since they deal with the more common genera of Amer- 

 ican forest trees. They were taken from Dr. Joseph Moeller's 

 "Anatomic der Baumrinden, " published in Berlin, 1882, which 

 gives detailed observations of a great many species including 

 a number of American trees. Whether a sufficient number of 

 species in each genus were studied to allow the generalization 

 of structure for the whole genus remains to be shown by fur- 

 ther work. No attempt was made in these notes to collect all 

 of the facts brought out concerning our American trees; the 

 idea of the author was to get a step further away from the 

 broad generalizations that are commonly found, by giving the 

 more prominent features of the genera. The characteristics 

 given hold good for the genus only in so far as they apply to 

 the species investigated. 



The bark is composed of three more or less distinct parts : 

 the outer bark includes all tissues outside the innermost layer 

 of phellogen ; the middle bark includes primary phloem and 

 the phelloderm of the innermost phellogen layer; the inner 

 bark, the secondary phloem inside the innermost layer of 

 phelloderm. 



Bark characters are not sufficiently distinct to make an 

 absolutely reliable key for identification. 



It cannot be doubted that the formation of "borke", the 

 scales and plates of bark on the outside of the tree, is not 

 governed by a certain stage of development but rather that 

 it is dependent on outside mechanical as well as physiological 

 influences. 



CONIFERAE. 



Outer bark. Most conifers develop the periderm during 

 the first vegetative period, and as a rule the epidermis falls 

 off soon afterward. Pinus and Taxodium keep the epidermis 



