PERFECT DEVELOPMENT OF POLLEN 
View of pollen sack of Crataegus coccinea, a hawthorn whose pollen shows no signs of sterility, 
practically every grain being perfect. 
that they did, although Brainerd had 
had no personal experience in raising 
them from the seed. 
As to the question, ‘‘ Will the different 
species hybridize?”’ Sargent had seen 
no evidence of it; Ashe thought that 
many did, and that ‘doubtless some 
of those called species are hybrids.’’(1). 
He did not think, however, that these 
hybrid forms were any more numerous 
in this genus than among the nearly 
related species of oaks. Beadle and 
Eggleston thought that they probably 
did, and Brainerd, although he had 
never hybridized any himself, knew of 
many cases that appeared to be natural 
hybrids—“‘local species, each quite inter- 
mediate between the supposed parents 
with which it is associated’”’ (1). Dun- 
(Fig. 7.) 
bar had seen no evidence of hybridizing, 
but thought it very possible. 
The last question as to whether the 
new species had arisen as mutations 
brought out extremely varied opinions. 
Sargent did not answer the question; 
Beadle thought that they had; Eggles- 
ton that some were hybrids and some 
were mutants; Ashe that probably 
some were mutants—‘‘some of the 
forms in the Molles group in Missouri 
and Illinois would seem to be mutations 
leading to the inference that some of the 
species in this group may have origi- 
nated in this manner. The variations 
in the Pruinosae in the Appalachians, 
and the localized valley species also 
indicate mutation origin” (1). Brainerd 
thought that there might be mutants, 
but it would be very hard to prove, and 
267 
