CAN THIS BE A GOOD SPECIES? 
Pollen grains of Crataegus cognata, highly magnified. A few of them are seen to be perfect, 
while an equal number are quite incapable of germination. 
If such a condition were 
found in the pollen of a single species, it might not attract great attention, but when 
hundreds of species, in the genus Crataegus, are found to have this kind of pollen, the 
botanist naturally inquires what has happened. 
Among the Pruinosee then, we find 
conditions much the same as in the 
rest of the genus—a relatively small 
proportion of the species showing normal 
pollen and more than half showing 
pollen markedly abortive. In view of 
the fact that unusual sterility and an 
unusual amount of variation are char- 
acteristic of hybrid races, the question 
of mutation among the Crataegi seems 
to resolve itself into a matter of hybrid- 
ization; and in fact, this is the conclu- 
sion which Mr. Brown reaches even 
without this important morphological 
evidence. 
In 1908 (1) he crossed the English 
hawthorn—C. monogyna—with the na- 
tive C. Brainerdi: in 1909, he and 
William Moore made cross pollinations 
between the majority of the native 
appearances 
(Fig. 17.) 
species with the result that in all cases 
the fruit set and matured, to all external 
entirely normal. The 
theory which he reached as a result of 
his investigation was that the enormous 
increase in the species of the genus is 
due to extensive hybridization since 
the dense forests have been cleared 
(2). The irregularity in the number of 
stamens and pistils, the variation in 
shape of leaves and color of anthers 
(from white to dark purple), the occur- 
rence of plants with characteristics of 
two different species which grow in the 
near neighborhood, and the occurrence 
of numerous local species—one of which 
is peculiar to almost all of the states 
east of the Mississippi—all these facts 
in his opinion point to extensive hybrid- 
ization. No sufficient tests have been 
277 
