WHERE TWO GROUPS OF HAWTHORNS OVERLAP 
Area perpendicularly shaded indicates range of Coccineae, while area horizontally shaded indi- 
cates range of Intricatae. 
normally at all, but appeared to be 
collapsed and quite lacking in contents. 
After embedding the C. praeclara flowers 
in celloidin, and after staining the 
sections cut with hematoxylin and 
safranin, examination of the pollen 
grains showed them as _ irregularly 
elongated, brownish colored bodies— 
greatly in contrast to the triangular, 
opaque, and thoroughly stained normal 
grains that one would expect to find in a 
pure species. In cases of this nature, 
the plant must be cross-fertilized before 
it can propagate its kind. 
Upon looking over 171 different forms 
of Crataegus, I found all degrees of 
pollen sterility. Thirty-five I classed as 
pure although many of them showed 
some grains of abortive pollen; sixty I 
classed as having from 10 to 50%; 
forty-one from 50 to 75%; and thirty- 
five from 75 to 100%. 
As a result of an examination of the 
171 specimens of Crataegus, I found the 
extraordinary state of affairs that 
roughly not quite one-fifth had normally 
developed pollen; while seventy-six (or 
(Fig. 11.) 
within nine of one-half the total number) 
had between 50 and 75% sterile pollen. 
It is only fair to add that these species 
were largely among forms of such 
comparatively recent appearance that 
a considerable proportion of them have 
not yet been described. Out of the 
most sterile group (from 75 to 100%) 
twenty of ‘the thirty-five species in the 
group could not be found in either 
Gray’s New Manual or Sargent’s Man- . 
ual of the Shrubs and Trees of North 
America; thirty-five of the forty-one 
species in the next group (50 to 75%) 
and twenty-nine out of the group with 
normal pollen, had not been described 
in either of these manuals. 
The Intricatae form one of the most 
interesting groups of the genus Cratae- 
gus: first because all the species of 
this class were once included in the 
Coccineae, before they were raised by 
Sargent to their present status; and 
second because an examination of the 
pollen of as many species as I could 
acquire among the two groups showed 
such contrasting results. 
cpl 
