CYTOLOGICAL STUDIES OF DIPLOID AND POLYPLOID 
FORMS IN RASPBERRIES 1 
By Albert E. LonglEy, Cytologist, Office of Biophysical Investigations , and George 
M. Darrow, Pomologist, Office of Horticultural Investigations , Bureau of Plant 
Industry , United States Department of Agriculture 
This investigation of the raspberries of the subgenus Idaeobatus 2 is 
a continuation of cytological studies of the pollen-mother-cell develop¬ 
ment of Rubus begun by the senior author in 192i. In the first investiga¬ 
tion, a report of which is now in press, the senior author found that diploid 
forms, that is, forms with a reduced number of seven bivalent chromo¬ 
somes, were the exception in the subgenus Eubatus. 
The present article presents the result of a careful study of the pollen- 
mother-cell development of species and varieties used in raspberry 
breeding by the Office of Horticultural Investigations of the United 
States Department of Agriculture, in which it is shown that most rasp¬ 
berries have seven bivalent chromosomes. 
The study was undertaken to determine the chromosome number of 
the various species of raspberries as an aid to breeding and especially to 
find some explanation for the peculiar behavior of hybrids of La France 
and Ranere (St. Regis) varieties. From 100 or more seedlings of this 
particular cross only one weak plant gave well-developed fruit. A 
large percentage (32) bore sterile flowers and the remainder showed a 
range in fertility from those having an occasional flower in which a 
drupelet set to those with several drupelets to each flower. La France 
has been considered a variety of Rubus idaeus , the European raspberry, 
and Ranere, a variety of R. strigosus , the American red raspberry. 
These species are more closely related than many others which, when 
hybridized, give all, or nearly all, fertile progeny. For example, hybrids 
of Gregg (R. occidentalis) X Ranere (R. strigosus) in the same environ¬ 
ment as La France X Ranere hybrids are entirely fertile. Certain other 
forms, when crossed, also gave an unexpectedly large percentage of 
infertile seedlings. Such results are difficult to interpret and it was hoped 
that knowledge of chromosome behavior might help to explain them. 
The subgenus Eubatus (blackberries) in which the haploid number is 
seven has many chromosome groups, that is, tetraploid, pentaploid, hexa- 
ploid, and octaploid ( 12 ). The closely related genus Rosa also has the 
same basic chromosome number seven and has similar chromosome 
groups (19) (j) (14). Hybrids between polyploidal forms of Rosa are 
reported to behave in a manner quite different from the simple Men- 
delian expectation. It was considered possible, therefore, that there 
were similar polyploidal groups among the raspberries which would 
explain the results observed. To make the work as systematic, compre- 
1 Received for publication Feb. 9, 1924. 
2 The classification used in this paper is, for the most part, that of Focke given in “Species Ruborum” ( 8 ) . 3 
8 Reference is made by number italic to “ Literature cited,” p. 747-748 
Journal of Agricultural Research, 
Washington, D. C. 
(737) 
VoL XXVII, No. jo 
Mar. 8, 1924 
Key No. G-380 
