THE JACK OAK* 



(Quercus elUpsoidalis) 



By William Trelease^ University of Illinois. 



Northwestward from the head of Lake Michigan the 

 usual sharp distinction between the red oak (Quercus 

 yifj)ra—0T maxima as people are disposed now to call it), 

 the scarlet oak (Q. coccinea) and the black oak (Q. vein- 

 Una) is confused by the occurrence of numerous trees that 

 present various types of fruit, rather like that of the 

 scarlet oak but sometimes suggesting that of the red oak, 

 associated with the multiform foliage for which the scarlet 

 and black oaks are noted. Typical red oak and black oak 

 trees very often occur associated with these aberrants : 

 and, except for an infrequent individual now and then 

 which suggests a hybrid, these suffice to indicate that the 

 questionable trees do not represent a transition by which 

 one of the usually recognized types blends into the other. 



Many years ago, Engelmann^ called attention to these 

 peculiar oaks which he was unable to identify elsewhere 

 than with that tree of the lower St. Lawrence to which the 

 younger Michaux^ gave the specific name amhigua, though, 

 being preoccupied for another oak, this name was replaced 

 by him shortly^ by horealis. A peculiar bulging or thick- 

 ening of the cup-scales of some of the northwestern oaks 

 was noted by Engelmann, who perhaps indicates his diffi- 

 culty in their identification when he frankly admits that 

 the fruit of amUgua as figured by Michaux does not re- 

 semble any form of gray-oak acorns he himself has seen. 



Though Engelmann was well acquainted with Dr. 

 George Vasey, then a resident of Illinois but editorially 

 connected with The American Entomologist and Botanist, 



*Presented in abstract before the Botanical Society of America and the Eco- 

 logical Society of America, December 29, 1916. 



1 Trans. Acad. Sci. St. Louis. 3 : 401 ; 4 : sx. 



« mst. Arb. Amer. 2 : 120. pi. 24, 1812. 



* N. A. Sylva. 1 : 81 ; — but the n&meamhigua remains on the plate, 26, and 

 the reason for using it originally is explained in the text. 



108 



