112 ILLINOIS ACADEMY OF SCIENCE 



Though not distinguished by a common name near the 

 limits of its range, it appears to be known in northwestern 

 Illinois as jack oak, — occasionally varied into black jack, 

 though not through confusion with the true black jack, 

 Q. marilandica. It is a tree of the timber fringe along 

 water courses in the flat prairie region, forms an abundant 

 constituent of similar belts flanking the more northern 

 rivers, and enters into the "oak openings" that are charac- 

 teristic of the rolling prairies of Wisconsin. 



This jack oak is a tree which closely resembles the black 

 oak (pi. 139), and, like the black oak, it holds its dried 

 foliage far into the winter, so that from a distance individ- 

 uals of these species may be picked out then when in groves 

 that contain a good deal of red oak. Though on the sandy 

 soil in its type locality it does not become very large, and 

 may fruit when scarcely ten feet high, it reaches a height 

 of sixty feet or more, with a trunk diameter of nearly three 

 feet, on the rich land in western Illinois, as about Morri- 

 son. More finely and densely branched than the red oak 

 usually is, in this respect resembling the pin oak and 

 black oak, it is less percurrent than the pin oak usually 

 becomes, and like the black oak and the pin oak it has 

 more glossy foliage than the red oak, and its leaves (pi. 

 141 ) are varying and prevailingly as deeply cut as those of 

 the pin oak or of the very variable black oak. In external 

 bark characters (pi. 140) , it stands between the red oak and 

 the black oak. Some trees have a smoother trunk than 

 most red oaks, but others are quite as rough as even any of 

 the associated black oak trees. Its inner bark lacks the 

 characteristic yellow coloration of that of the black oak. 



As Oersted insisted long ago, and as I have shown for 

 our black oaks collectively,* and Miss Cobb for our eastern 

 white oaks,t the mature buds of oaks afford fairly depend- 

 able specific characters. In this respect, Quercus ellip- 

 soidalis stands out distinctly among the oaks that it occurs 

 w^ith (pi. 143). Quercus palustris, which barely enters its 

 range from the south, is readily known by its rather 

 small conical glabrous brown buds; Q. maxima by its 

 much larger equally glabrous red-brown buds; and 

 Q. velutina, by its still larger often 5-angled or 5-grooved 



*Proc. Amer. Philosoph. Soc. 51 :167-171. pi. 10-13. 

 tProc, Amer. Philosoph. Soc. 54165-174. pL 4-6. 



