Mar. 8, 1924 
Diploid and Polyploid Forms in Raspberries 
745 
formed a compact mass in which no pollen was formed.” Form No. 2 
was more fertile, as the anthers pictured in Plate i,B, show. From this 
plant there was procured sufficient material for a study of the reduction 
division. Since this hybrid is triploid, it corresponds to the intergroup 
crosses of wheat (Triticum) in which Sax (17) found the greatest sterility. 
It indicates that the sex cell on La France side had 14 chromosomes. 
The behavior in egg formation, therefore, differs from that studied by 
Tackholm for the Canina group of roses. He found that the viable egg 
of a tetraploid species had 21 chromosomes and the viable pollen usually 
had 7 chromosomes. 
It seems certain that this list of polyploid raspberries is not complete. 
The varieties Buckeye, Hailsham, and Souvenir de Desire Bruneau show 
external characteristics which place them in this group, that is, as grown in 
the United States, they are more hardy than the diploid varieties of 
R. idaeus , have heavy dark green foliage, resist leaf spot, and bear fruit 
on young canes in autumn. 
DISCUSSION 
POLLEN STERILITY IN RASPBERRIES 
Table I shows a dozen diploid forms in which the per cent of good 
pollen has been determined. Five of these diploid varieties are hybrids, 
and the large amount of sterile pollen existing in them, in contrast to 
the small amount of sterile pollen that generally exists in stable species, 
supports the view that hybridizing may cause noticeable sterility in the 
offspring (jo). 
This table also shows a second group of sterile raspberries, including 
all but two of the polyploidous forms. The high percentage of good 
pollen found in the two exceptions was unexpected, and since a study of 
these varieties is not complete, no explanation will be attempted. The 
remaining six forms are very sterile and characterized by an unequal 
distribution of the chromosomes during the pollen tetrad formation. 
This extreme sterility may be attributed to unbalanced chromosome 
conditions existing in the nucleus of the pollen grain, which in turn is 
recognized as a character of hybrids between incompatible species. The 
inference, therefore, seems to be that raspberries showing pollen sterility 
are of hybrid origin and that polyploidous raspberries are the result of 
crosses between plants belonging to different chromosome groups. 
CHROMOSOME MULTIPLICATION DUE TO HYBRIDIZATION 
Polyploidy in raspberries seems to have originated in both Europe and 
America. Our knowledge is too limited to allow the acceptance of one 
explanation to the exclusion of all others as to how it originated, but the 
present data support the theory that polyploidism in raspberries has 
originated through hybridization. 
In England Rubus caesius y a tetraploid trailing blackberry, blossoms 
at approximately the same season as the raspberries, while the common 
blackberries blossom several weeks later than the usual raspberry flowering 
season. A species with dark thick leaves, similar to R . caesius , seems 
essential to explain the characters present in polyploid raspberries. 
One English autumn-bearing raspberry was reported as a hybrid, R. 
caesius X R. idaeus (n). The junior author has raised many R. idaeus X 
