746 
Journal of Agricultural Research voi. xxvn, no. io 
R. caesius crosses from seed and obtained a great variety of forms, but 
unfortunately these F x plants had been destroyed previous to this study 
and no cytological material is available. 
An F 3 hybrid, originated by Professor Ness {13) of the Texas Experi¬ 
ment Station, is a cross between the Cardinal raspberry, a diploid form, 
and R. rubrisetus , a southern blackberry. A cytological study of this 
hybrid seems to provide evidence to support the theory of the origin of 
polyploidism in raspberries through hybridization and selection. 
Three figures drawn from early reduction phases of this F 3 hybrid show 
the cytological conditions in this hybrid. Plate 3, J and K, shows the 14 
chromosomes of this tetraploid form, while Plate 3, L, pictures a slight 
irregularity in chromosome distribution. It was exceptional to find 
irregularities during meiosis, but the history of this hybrid shows that it 
has been selected through several generations and now behaves like a 
stable species. 
This F 3 hybrid demonstrates that fertile raspberry-blackberry hy¬ 
brids are possible and it also shows that a tetraploid Rubus has been 
experimentally produced with the characteristics of a stable species. 
After studying many known raspberry X raspberry hybrids without 
finding a single case of chromosome multiplication it seems worth while 
to consider the possibility that all the polyploidous forms described in 
this article are the result of raspberry X blackberry hybrids that have 
been selected artificially or naturally and now have found a place in 
our commercial varieties of raspberries. 
SIGNIFICANCE OF DIPLOID, TRIPLOID, AND TETRAPLOID RASPBERRIES 
We have shown that all the species or varieties of raspberries examined 
have the basic chromosome number seven. Furthermore, hybrids even 
between species which are quite different in their external characters 
also have the same basic number seven. A few varieties referred to R. 
idaeus i however, are triploid or tetraploid and the presence of these few 
variant forms, in a group otherwise uniform in this respect, is important. 
There are genera in which chromosome multiplication has been re¬ 
ported, and in which new hybrid species and varieties are appearing 
continually. The blackberries, roses, and hawthorns are well known 
examples where multiplication of species and varieties is associated with 
chromosome multiplication. In Europe several thousand Eubatus Rubi 
have been collected and described as species while the recent American 
publication on “Standardized Plant Names” (z), devotes 50 pages to 
listing varieties of roses alone. The presence of a few polyploid rasp¬ 
berries, of unquestionably recent origin, may be the beginning of a 
similar multiplication in raspberry forms. All polyploidous raspberries 
belong to the best autumn-fruiting European group, and, therefore, an 
effort should be made to combine by hybridization their good qualities 
with those of our hardy American varieties. 
Ea France X Ranere hybrids, obtained at the Bell station by the junior 
author demonstrate the variable results that may be expected from inter¬ 
group hybrids. The raspberry breeder who attempts to introduce the 
characters present in polyploid raspberries by hybridization will find his 
efforts seriously limited by the incompatibility frequently existing be¬ 
tween hybrids involving different chromosome groups. 
The recent study of tetraploid Datura hybrids ( 4 ) is a carefully planned 
scientific research into the genetic behavior of a recently discovered 
