1907] MACDOUGAL—HYBRIDIZATION OF WILD PLANTS 53 
tion of these two forms. Taking this conclusion as established, it 
may then be said that the name Q. heterophylla is at present applied 
to a medley of oak trees which possibly includes the first generation 
of a cross between Q. rubra and Q. Phellos, secondary hybrids with 
either parent, as well as successive generations in which various 
combinations of ancestral qualities may appear. 
Another aspect of the parental form of the above hybrid and 
the progeny remains to be mentioned. A collector covering the field 
occupied by the hybrid in which the parental forms come into contact, 
who gathered a full series of material from the trees available, would 
have data upon which mistaken conclusions as to intergradation of 
species by fluctuating variability might be made. This leads to the 
Suggestion that any supposed intergradation of two species of seed- 
plants should be examined with respect to possible hybridizations 
before any final estimate is reached in the matter. 
Furthermore, it is to be seen that while in all reasonable probability 
opportunity for hybridization between these two oaks has been pres- 
ent for a period of unknown but undoubted great length, it has not 
resulted in anything in the way of occurrence or distribution suggestive 
of the disappearance of either parental form. The probably greater 
frequency of intra-specific fertilization over hybridization would secure 
this result. Then again it is to be seen that even in the case of com- 
Plete cross-fertilization of all of the individuals there would be the 
Probable reconstruction of the ancestral forms among the progenies. 
Quercus Rudkinii has long been reputed to be a hybrid between 
Q. Phellos and Q. marylandica, and a visit was made to the group 
of trees from which the species was originally described by Dr. 
Britton, in company with him and other botanists in October 1905. 
These trees stand near Cliffwood, New Jersey, and since the original 
discovery in 1881 others have been found on Staten Island and also 
to some distance to the southwestward in New Jersey. The mere 
facts of distributional relations together with the anatomical features 
offered by the bark and leaves led to the description of these trees 
as being of a hybrid origin from the willow oak and the black oak. 
If these facts only are taken into account, it seems quite as plausible 
to regard this tree as a hybrid as Q. heterophylla. The leaves from 
the included trees showed a range of forms that included the type 
