176 The Botanical Gazette. [May, 
out in the struggle for existence; one of the provisions of 
nature to keep the species distinct; or, as Dr. Gray suggests, 
fertilization by one of the parents may soon extinguish the 
hybrid characters.” ® 
To those who question the hybridity of these oaks, and 
deem such forms varieties of closely related but very variable 
species, the answer may be made that, since hybridizing is a 
frequent resort of the horticulturist for the production of new 
varieties of plants, it is to be expected that something of the 
same kind will occur in nature where plants nearly related 
grow together promiscuously. As such crosses are effected 
by dusting the stigma of one species or variety with the pollen 
of another species or variety of the same genus, or in the case 
of bigeneric hybrids, of a different genus, similar results may 
be looked for among wild plants where this dusting must 
often occur whether effective or not. But it is in the highest 
degree efficient for plants of the same species to be cross 
fertilized, and in many cases it is the sole method of fertility 
It is done on so large a scale by various agencies that out 
surprise should not be at finding spontaneous hybrids, but 
that they are seemingly so rare in wild plants. Failure to 
produce them has to be ascribed to other causes than the 
lack of opportunity. And it is in genera with dicecious, and 
often anemophilous, flowers, such as Carex, Quercus and 5a- 
lix, that hybrids have most frequently been detected in nature. 7 
Especially is this the case with willows.7 With such eg 
the conditions are least complex, and the opportunities wa 
hybridizing most frequent. at has 
These oaks plainly show the marks of hybridism oI , 
have been noted by various observers, and summarize y 
Sachs, among which the two following closely apply: (4) Af 
hybrid is possessed of external characters intermediate 
be- 
tween those of its parent forms, usually nearly a ie rule 
re eee 
tween. (4)Thecl teristics of the parent-forms ar both 
so transmitted to the hybrid that the influence of die 
ion of the 
ferent peculiarities. ”® | 
: ybridity for these 
It is also very strongly in favor of their hy aa" 7 
®Botanical Works, 403. ae willows 
"Insects, especially bees, take an active part in the pollination ode Be 
Wimmer, Salices Europaeae, Introduction, p. xlviii. Ib. Wildw 
tardpflanzen, 144. 
®Lehrbuch (4th ed.) 891. Text Book, 917. 
