

Hill : Celtis pumila Pursh 501 



Celtis pumila. Fig. 3 



Nutlet white, 5.5-6 x 5—5. 5 mm., globose or nearly spherical, 

 being slightly higher than wide, bluntly apiculate. Surface 

 coarsely reticulated, the pits shallow, the bordering walls broad 

 and rounded. 



Celtis Mississippiensis. Fig. 4 



Nutlet yellowish-white, 5x5 mm., globular, minutely apicu- 

 late. Surface reticulations irregular, the pits deeper and bordering 

 walls sharper than in the others. 



Another form, not figured, is worthy of notice. It is from a 

 specimen in the herb, of the Field Columbian Museum, no. 63720, 

 C. occidentalis L., coll. J. R. Lowrie, 1874, " barrens of Hunting- 

 don Co., Pa." The nutlet is globose, a little higher than wide, 

 6.5 x 5 mm., in size and shape between that of C. pumila and 

 occidentalis, light tan-colored. The reticulations, pits and their 

 bordering walls are similar to those of occidentalis. The leaves are 

 thinnish, larger than in C. pumila, slightly serrate, shaped much as 

 in C. occidentalis. The specimen shows a branching rather spread- 

 ing or divaricate, akin to that of shrubs in the dune region of 



Indiana. It has characters intermediate between Celtis pumila and 

 C. occidentalis, but nearer the latter. It may be distinct but the 

 material is too scanty to decide. Hybridity is also suggested. 



My experience with the floral habits of the two species of our 

 region in 1898 and 1899 well illustrates their difference and is 

 worthy of record for its ecological bearings. It is a matter of 

 long observation that the cold air of Lake Michigan retards the 

 anthesis of plants growing near the shore. There may be a differ- 

 ence of a week within a distance of ten miles, as seen in the same 

 species growing by the Desplaines River, about that distance away. 

 Celtis pumila in the dune region is from one fourth to one half a 

 mile from the shore. C occidentalis at Wolf Lake and vicinity is 

 from two to three miles from the shore. C. occidentalis along the 

 Desplaines is about eleven miles from the lake. On April 28, 1 899, 

 this was collected at Wolf Lake in full bloom, the trees being yellow 

 with the flowers. The day after those at May wood on the Desplaines 

 were examined. The staminate flowers had nearly all fallen off, 

 s howing that the anthesis would have been in the condition of 



