1902.] NATURAL SCIENCES OF PHILADELPHIA. 33 



CONTKIBUTIONS TO THE LIFE-HISTORY OF PLANTS, NO. XVI. 

 by thomas meeiian.' 



The Bartram Oak, in Connection with Variation and 

 Hybridism. 



My recent di.?covery that the mature wood of tree.«i may so change 

 their original lines as to alter the v.hole form of the skeleton, and 

 that these changes in form are characteristic of the species, may 

 enable us to settle some disputed questions. In the case, somewhat 

 famous, of the Bartram oak, Qiiercus heterophylla Mx., we may 

 now say with absolute certainty that it is but a form of the pin oak, 

 Quercas palustris. The angular divergence of the mature branches 

 is the same in both ; while other resemblances to the latter species 

 are well known. ]Much of the confusion in regard to this matter has 

 arisen from the tree, still in the Bartram gardens, that for many 

 years past has been pointed out to botanists as a seedling from the 

 original tree long since destroyed. Specimens from this tree are 

 widely diffused through herbariums. It is but a somewhat lobed- 

 leaved form of the willow oak, Quercus Phellos, a condition not 

 infrequent among trees of this species, and of which form there are 

 numerous specimens in the herbarium of the Academy of Natural 

 Sciences of Philadelphia. If any one had thought to compare 

 these specimens with the plate in Michaux's " Sylva," the error 

 would have been noted. Dr. Engelmann was familiar with 

 Michaux's plant only through these misleading Bartram specimens, 

 and Iience described his Quer'CUi palustris-imbricaria, whicli proves 

 to be identical with ^Michaux's Q. heterophylla. Dr. Engelmann 

 was led to write positively in regaixl to the hybridity iii a great 

 degree from his belief in the sterility of hybrids — the St. Louis 

 tree producing only a single acorn, so far as any one knew, during 



' The manuscript of this article was found among the late Mr. Mee- 

 han's papers after his death and sent to the Academy for publication by 

 his son, ]Mr. S. Mendelson Median. It possesses a special interest as 

 bein^ the last contribution from one who for nearly forty years enriched 

 the Proceedinr/s with the results of his acute and devoted study of 

 nature. Mr. ]\Ieehan's first paper in the Proceedings of the Academy 

 was published in 18G2.— Editor. 



