THE POLLEN OF CRATAEGUS HARBISONI 
The pollen illustrated in Fig. 9 is here shown still more highly magnified. 
It will be seen that 
the empty grains fold up very neatly, their envelopes being provided with creases for that 
(Fig. 16.) 
purposes. 
of which forty-two were strictly local 
in their distribution. Red Mountain 
being in northern central Alabama, I 
found that in this area, even when I 
limited the count to those forms which 
grew in upland woods, there were still 
thirty different species; and of these 
thirty, twenty-two were extremely local. 
Here again in the case of C. venusta, 
we seem to find ideal conditions for 
natural hybridization combined with a 
high degree of spore sterility. 
In answer to Mr. Brown’s question 
in regard to mutation in this genus, 
Ashe cites the Pruinosae and Molles 
groups as showing some indication of 
its presence. Since the Molles have 
only one of their species native to 
Massachusetts, I have made no study 
of them; but I was able to secure a 
number of the Pruinosae, and as to 
pollen sterility they seem to exemplify 
the conditions of the genus as a whole. 
In Gray’s Manual (1908) to the 
276 
Pruinosae are ascribed six species and 
eight varieties of which all but C. 
pruinosa var. dissona and C. pruinosa 
var. philadelphica are considered close 
enough to species to constitute a 
separate paragraph. Varieties which 
are placed in this category are thought 
“so distinct and peculiar that they are 
not unlikely to establish the claim” 
and be considered species. In fact this 
prediction has largely come true; as of 
these eight varieties, Sargent describes 
seven as species and only one—var. 
dissona—as a true variety. The results 
of the investigation of the Pruinosae was 
as follows: 
% of 
Sargent Gray abortion 
C. cognata var. latisepala 1S 
C. pruinosa C. pruinosa 60 
C. robbinsiana_ var. beckwithia 50 
C. deltoides C. deltoides 50 
C. fusca var. philadelphica 40 
C. conjuncta var. conjuncta practically 
pure 
Forma dissona Forma dissona practically 
pure 
