138 PROCEEDINGS OF THE ACADEMY OF 



August 4. 

 The President, Dr. Ruschenberger, in the chair. 

 Six members present. 



Dimorphisvi in the Leaves of Acer Pennsylvanicinn., Lin. 

 Mr. Thomas Meehan exhibited some branches of Acer Pennsyl- 

 vanicnra, Lin. (A. striatum, Lamb), which had a remarkable sys- 

 tem of dimorphic foliage, and which he believed had been gener- 

 ally overlooked. 



The first pair of leaves developed after the bursting of the bud 

 in the spring, were larger and more perfectly developed than any 

 subsequent ones. In his specimens thej' were about six inches 

 long and five wide, and stronglj^ three-lobed towards the apex. 

 The next pair, however, were usually lance linear, in the specimens 

 exhibited about five inches long and less than two wide. Occa- 

 sionally there was a tendency to the pi'oduction of a pair of lobes, 

 but usually the margins were entire or sparsel}^ serulated. The 

 third and subsequent pairs of leaves partook of the form of the first 

 pair, though seldom so large. He had examined sevei'al hundred 

 of young ti'ees, and all had this singular dimorphic condition, the 

 second pair in all cases having this peculiar narrow form. 



It was worthy of remark that in plants with alternate leaves, the 

 leaves with their axial buds were generally about the same size. 

 In some few instances there were variations in the size, especially 

 in the one-third arrangement of the leaves on the stem. In oppo- 

 site leaved plants the rule was the other way ; one bud or one leaf, 

 either in the blade or petiole, being larger or longer than the other. 

 In the maples this was especially the case. At times the petioles 

 in some cases would be not more than half the length opposite. He 

 had found this especial peculiarity, however, in no other species 

 but A. Pennsylxianicum that he had been able to examine, which 

 included most in common cultivation. It might be in A. spicatum, 

 Lam., which he had not been able to examine this season, and 

 which he supposed to be but a variety of A. Pennsylvanicum. 



August 11. 

 The President, Dr. Ruschenberger, in the chair. 

 Seven members present. 



