502 
ever, the abnormalities seen in the cell 
divisions in the mule testis are not pre- 
cise in nature, but occur in a haphazard 
fashion, as a result of a tangled con- 
fusion of cell elements—it is not incon- 
ceivable that a chance series of divisions 
might give rise to a germ cell able to 
cause conception in a fertile female. 
Moreover, it must be noted that it is 
extremely seldom indeed that male 
mules are allowed to come to the age of 
maturity without castration, and it is 
even more seldom that they are allowed 
to breed mares. Therefore there is very 
slight opportunity to put their breeding 
powers to a test. 
It should be further remembered that 
in practically every case these micro- 
scopic studies have been made on the 
germ gland of the male. It is conceiv- 
able that matters might occasionally 
proceed differently in the ovary, where 
a different chromosome constellation 
exists. This would result in a condition 
where female mules might at rare inter- 
vals possess generative powers but 
males never. 
There may be some uses for which a 
mule that is only 144 horse might prove 
valuable, and certain it is that there are 
many occasions where a mule that is 
only 44 ass would be welcomed with 
The Journal of Heredity 
relief and joy. But such animals are 
not as yet staple market commodities, 
for whatever the true situation in regard 
to mules occasionally producing off- 
spring may be, one thing remains cer- 
tain, namely, that as far as the breeding 
industry is concerned, we must as yet 
take our mules half-and-half in the way 
that Homer and Varro described several 
thousand years ago. 
LIST OF REFERENCES 
AYRAULT, EuGENE.—De 1’Industrie Mulas- 
si¢re. 
Ewart, Cossar.—1899. Penycuick Experi- 
ments. 
Guyer, M. 
Normal and Hybrid Pigeons. 
cinnati, Bulletin 22. 
F.—1900. Spermatogenesis of 
Univ. Cin- 
IwAnorF, E.—1915. Untersuchungen tber 
die Ursachen der Unfruchtbarkeit von 
Zebroiden. Biol. Cent. 25: 789-804. 
SANSON, ANDRE.—1888. Traité de Zodtechnie, 
Tomes 3-5. 
SHAILER, N. S.—1895. 
mals. 
STEPHAN.—1902. Sur la structure histologique 
du testicule des Mulets. C. R. d 1’Assoc. 
d’Anat. IV, Montpellier (quoted by Iwanoff). 
TEGETMEIER, W. B. and SUTHERLAND, C. L.— 
1895. Horses, Asses, Zebras, Mules and 
Mule Breeding. London. 
WHITEHEAD, R. H.—1908. Function of Inter- 
stitial Cells of Testes. Anat. Rec. 2:177. 
WODSEDALEK, J. E.—1916. Causes of Sterility 
in the Mule. Biol. Bulletin XXX: 40, 
pls. i-x. : 
Domesticated Ani- 
IRIS BREEDING 
students of genetics, probably be- 
cause other plants can be grown in 
less space and time. Pollinations 
are easily made, however, and any 
amateur of this genus might well try 
his hand at crossing some of his favorite 
forms. Miss Grace Sturtevant of Wel- 
lesley Farms, Mass., contributes the 
following suggestions of technique: 
“The irises with which I have worked 
have been the hardy varieties which 
could be grown without protection or 
especial treatment in my garden; thus 
limiting the scope of the crossing in a 
large degree to what are known as 
German irises, though truth to tell I 
| suze have been little used by 
have yet to obtain a seed from a real 
German iris. 
“The method of procedure is simple. 
I remove the stamens from the bloom 
to be cross-fertilized, before the pollen 
sacs open, and apply pollen to the lip 
of the stigma by rubbing it with a 
pollen-laden anther from the bloom 
used in making the cross. This covers 
the surface with pollen so well that there 
is little danger from other pollen, but 
to make matters sure the bloom can be 
protected for a short time, or the falls 
removed so that no wandering bee can 
crawl in beneath the arching style-arm. 
I usually remove the rest of the buds 
on that branch and label it. 
