338 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 
by a parasitic fungus that, in spite of all effort, it died at a end of its 
second year, and before flowering. . 
These have been my most instructive experiments. What has been 
done with Geraniums and other florists’ flowers has still been instructive 
in this, that hybrids are just as fertile, and the pollen just as potent, as in 
the original species. Barrenness occurs as often among individuals of 
pure species as among the progeny of individuals resulting from hybrid- 
isation. Sterility results from some physiological law, of which pollen- 
isation is but an incident. 
In regard to the supposed sterility of hybrids, Dr. Engelmann describes 
in his well-known paper on American Oaks a number of supposed hybrids 
in nature. In one case, Quercus palustris x imbricaria, he cites its 
sterility in evidence. Before the tree was destroyed by a railroad track he 
found a solitary acorn. This grew and is nowa large tree on my grounds, 
and is of exceptional fertility, producing a large crop of acorns of pure 
Quercus palustris, and with the foliage and habit of the same species, 
though there are numerous leaves entire, as in imbricaria, but in venation 
and all other characters it is wholly Quercus palustris. 
Though hybrids in nature are probable, we have little direct evidence 
of the fact. ‘The occurrence of intermediate forms, or of sterility in some 
cases, is no evidence, especially when we know of the wide range of varia- 
tion in such cases, for instance, as in monotypic species, where cross-pol- 
lenation is out of the question. 
