310 A CYTOLOGICAL INVESTIGATION OF SOME SPECIES 
get for these hybrids a chromosome-number very different from that 
which FRANCK found in the case of his hybrid individual 234 POJ, 
which, unfortunately, I could not investigate as it is no longer present 
in the collection of the experiment-station. 
CHAPTER V 
THE CYTOLOGY OF OTHER SPECIES-HYBRIDS IN CONNEXION WITH THOSE 
OF THE GENUS SACCHARUM 
In the litterature no cases are known in which hybrids with a larger 
chromosomenumber resulted from a cross, in the way which I suppose 
to have occurred in the species-hybrids within the genus Saccharum 
of which the preceeding chapter treated. ERNST gives in his book: 
„Bastardierung als Ursache der Apogamie im Pflanzenreich’’ the fol- 
lowing subdivision of hybrids: 
Group | Hybrids, the diploid chromosomenumber of which is equal 
to the sum of the chromosomenumbers of the two gametes 
which. fused. 
a. hybrids from gametes with equal chromosomenumbers: 
iso-diploid-hybrids ; 
b. hybrids from gametes with unequal chromosomenum- 
bers- heterodiploid hybrids. 
Group 2 Hybrids, the chromosomenumber of wihch is equal to the 
sum of the diploid chromosomenumbers of the parents: 
tetraploid hybrids. 
Hybrids with an isodiploid chromosomenumber usually possess in 
their haploid phase, a chromosome number equal to the haploid chro- 
mosomenumber of both parents. Usually unpaired chromosomes do 
not occur in the prophase of the division of the gonotokonts. Among 
these hybrids both fertile and sterile forms occur. 
Among the hetero-diploid hybrids various cases occur: 
1°. All chromosomes fail to pair in the gonotokonts. This case has 
been described by FRAU HAASE-BESSELL1) in the hybrids between Digi- 
talis purpurea and D. lutea which respectively have 24 and 48 chromo- 
somes in the haploid phase. These hybrids showed, during diakinesis, 
1) GERTRUD HaasE-BESSELL. Digitalis-Studien I. Zschr. f. ind. Abst. u. Ver- 
erbungslehre. Bd. XVI. 1916. 




