ELLIOTT: VARIATIONS OF QUERCUS. 53 



OLDER WOOD AND BARK. 



In the study of the more mature stem sections were taken 

 from the oldest material at hand. The cross sections showed 

 that the differences in thickness of bark persisted, but that 

 the relative increase in thickness of bark due to the cambium 

 ring was about the same. The original bast ring of No. 2 

 remained entire for at least seven years. That of No. 4 was 

 unbroken at three years. (Older material not available.) The 

 bast ring of No. 3 was broken up in the four-year-old stem. 

 That of No. 1 was never entire. (Figs. 61 to 64.) 



No. 1 showed the slowest growth of xylem and No. 3 the 

 most rapid, from trees very nearly all the same size. Cross 

 sections of the wood showed nothing that would distinguish 

 any one of the oaks except that the medullary rays of Nos. 

 1 and 2 were wider than those of Nos. 3 and 4. (Figs. 65 to 

 68.) In tangential section this showed much more clearly 

 and was an identifying characteristic. The sections were 

 taken from growth of the same year. (Figs. 57 to 60.) In 

 the same area (1.04 sq. mm.), the number of medullary rays 

 was as follows: No. 1, 129; No. 2, 63; No. 3, 134; No. 4, 144. 

 The difference between Nos. 1 and 4 was least pronounced. 

 No. 3 could be immediately identified by its very narrow rays, 

 and No. 2 by its large, broad ones. 



Macerations of the wood and bark revealed no distinguish- 

 ing characteristics. 



SUMMARY. 



The four oaks under consideration, classified as all being 

 Q. muhlenbergii, show some difference in general appearance 

 of leaves and acorns. The histology of the leaf reveals con- 

 stant identifying differences in epidermal hairs, number of 

 stomata, and size of epidermal cells, any one feature of which 

 will distinguish any one individual from all of the others. In 

 addition to these features which are different in each oak, 

 No. 4 is distinguished by wavy-walled cells of the lower epi- 

 dermis; No. 1 by thin-walled epidermis, and No. 2 by closely 

 packed palisade cells. The manner of ending of the middle 

 vascular bundle of the midrib differentiates No. 4, and the 

 place of ending differentiates No. 2. 



There is a difference in the sizes of the starch grains in the 

 seeds. No. 2 is characterized by the presence of the most 

 protein in the seeds. 



3 — Univ. Sci. Bull., Vol. IX, No. 4. 



