278 
made, however, to prove beyond a 
doubt whether or not hybrids of 
Crataegus are stable—circumstantial 
evidence seems to indicate that they are, 
but no such extensive experiments in 
breeding as would be necessary have 
been attempted on account of the 
difficulties due to the slow maturation 
of the plant. 
STUDY OF THE ROSE FAMILY 
Since Mr. Brown’s article in the 
Bulletin of the Torrey Botanical Club 
wast published, nevertheless, work 
carried on in the Harvard laboratories 
under Prof. E. C. Jeffrey by C. S. Hoar 
on the raspberries, and by Miss R. D. 
Cole on the roses, and also my own 
examination of the hawthorns, have 
revealed among the Rosaceae a large 
number of hidden or crypthybrids which 
are constant in their character and which 
are recognized by systematic botanists 
as good species, but which may be 
distinguished from normal species by 
the sterility of their reproductive cells. 
These crypthybrids, while they are 
extremely important from the evolu- 
tionary standpoint on account of their 
enormous variability and the consequent 
multiplication of species, must never- 
theless not be given credit for the origin 
of species. Although in answer to Mr. 
Brown’s questions Ashe, Beadle and 
Eggleston appeared to favor the idea 
that at least some of the new species of 
Crataegus might be mutants, investiga- 
tion of the morphological character- 
istics of the genus backs up Brainerd in 
his emphasis of the extraordinary tend- 
ency towards hybridization among the 
Rosaceae. I quote what he had to say 
on the subject (1). 
“In Europe the few species [of 
Crataegus] cross in many ways (Focke’s 
Pflanzen-mischlinge p. 146). I know 
of many cases which appear to be 
natural hybrids or local species each 
quite intermediate between the two 
supposed parents with which it is 
associated. The Rosaceae are of all 
others the most disposed to hybridize. 
I should expect the same in Crataegus 
as in Rosa, Rubus, Geum, Amelanchier 
and Malus. The condition in Crataegus 
is much like Rubus, Rosa and Viola. 
The Journal of Heredity 
The multiplication of even stable forms 
that may result (in the working out of 
Mendel’s laws) from one pair of parents 
is astonishing.”’ 
To summarize the evidence set forth 
in this paper, we find among the 
Crataegi an extraordinary amount of 
comparatively recent multiplication of 
forms; we find also, large numbers of 
local species combined with unusual 
sterility. Out of the 171 specimens 
examined only thirty-five could be 
considered uncontaminated with regard 
to pollen conditions, while seventy-six 
showed from 50 to 100% of abortive 
grains. Sterility partial or complete of 
the reproductive cells has long been 
recognized as a characteristic of hybrid- 
ism; and forms which are ordinarily 
accepted as species frequently reveal 
past genetical contamination by pollen 
infertility. Among the Rosaceae, a 
family showing an unusually strong 
tendency to hybridize, examination of 
the pollen conditions discloses a great 
number of these hidden hybrids. 
The Intricatae on account of their 
unique position seemed worthy of study 
in this connection. In the first place 
they are a relatively new group so 
closely allied to the Coccineae that they 
are included in the group as far as they 
were known to the older systematists. 
They show a smaller range of distribu- 
tion both collectively and individually 
than do the Coccineae; they only occur 
in localities where there is a possibility 
of crossing; and they have a degree of 
sterility unusual even for the genus 
Crataegus. This seems a_ suspicious 
combination of facts. Investigation of 
the other groups in so far as I could get 
material, parallels the condition found 
in these two groups—that among the 
more widely distributed species the 
pollen is apt to be good, while in those of 
more local range the pollen is largely 
abortive. This evidence is exemplified 
by C. venusta—a form extremely local 
in its range and growing under circum- 
stances ideal for cross fertilization— 
which proved to be 75% sterile. 
The study of this genus has brought 
out evidence of both systematic and 
morphological character to indicate the 
