ENGELMANN — OAKS OI THE UNITED STATES. 399 



J~>. alba X stellata. A specimen from the same careful observer (Bebb, 

 No. 24) must, I believe, be referred here. Leaves similar to those of alba, 

 with the narrow lobes occasionally widened forward and retuse, after the 

 manner of stellata, pubescent on the under side, as well as petioles, branch- 

 lets, and shallow cups ; cup scales distinct and regular but considerably 

 tumified at base ; in alba these scales are almost entirely changed into very 

 prominent knobs with short obtuse membranaceous tips ; in stellata they 

 are lanceolate, very distinct, only slightly tumified, and more canescent. 

 Bark and flowers of Mr. Bebb's tree are unknown to me. 



Specimens from South Carolina, sent by Dr. Mellichamp, mentioned 

 p. 389, seem to indicate other hybrid forms of the same parents. One has 

 the leaves and furrowed bark of stellata, but the glabrous branchlets and 

 glabrous anthers of alba. The other's bark is flaky like that of alba ; the 

 branchlets, the sinuate or obtusely-lobed leaves, and young acorns, are 

 glabrous; anthers unknown. Of neither have I seen the fruit. 



Q. alba X Prinus. A single tree, now unfortunately destroyed, was 

 observed by Dr. G. Vasey near Washington. Bark " rougher and darker 

 than in alba'; leaves incised-serrate, of firm texture, glossy above, pale 

 and slightly pubescent beneath ; hemispherical cups with distinct tumid 

 scales terminating in triangular membranaceous tips. The leaves are more 

 those of Prinus than alba, the acorns belong rather to the latter. Both 

 supposed parents grew with it on a gravelly hillside. 



The hybrid Black-oaks are much more numerous, or, to speak 

 more correctly, more have thus far been noticed, perhaps because 

 their leaf-forms are more various, and thus the intermediate ones 

 are more easily recognized. The mixture of entire-leaved with 

 lobe-leaved forms would of course be most readily discovered from 

 the intermediate leaf- form of the illegitimate offspring ; but it 

 remains for further close examination to ascertain whether lobe- 

 leaved species do not hybridize among themselves as well, or 

 entire-leaved forms also mix together, producing offspring of less 

 strikingly marked characteristics. 



That we have to look for one of the parents of three of our hybrids 

 to one and the same species, seems to correspond well with other 

 observations, all pointing to the fact that some species of a genus 

 are more prone to hybridize than others. This is true of Verbena, 

 hybrids of which abound in this neighborhood in numerous forms 

 as well as in a great many individuals ; of most of them V. stricta 

 appears to be one of the parents, perhaps because one of the most 

 common species, or from some innate quality which makes it 

 mix more readily with others ; perhaps from a peculiar structure 



