and of other related Primula Hybrids . 381 
appear in their 2 x number, namely 21 . No pairing of homologous chromo- 
somes ensues, but 10 move off to one pole and 11 to the other. ‘ The 10-11 
segregation of chromosomes in the formation of the germ cells of this 
hybrid shows that there is not here a pairing and separation of homologous 
chromosomes of maternal and paternal origin, but that the segregation 
tends to be into two numerically equal groups ’ (p. 195). 
The hybrid fern Polypodium Schneideri ( 12 ) furnishes another example 
of an inequality in the number of the parental chromosomes, one parent 
having a far higher number than the other. The parent P. aureum 
has 35 (x) chromosomes, the other parent, P. vulgar e , var. elegantissimum , 
has about 90 (x) chromosomes, and the number of chromosomes appearing 
at meiosis in the hybrid P. Schneideri varies from 95 to 125. This 
figure can only be considered as an approximate estimate, as the chromo- 
somes are so irregular and numerous, whilst at diakinesis some are 
apparently bivalent, and others univalent, that it is impossible to make 
an accurate count. The peculiar amitosis which is of such common 
occurrence in hybrids, and which may occasionally be found in pure 
strains, is frequently met with in P. Schneideri , dividing the pollen mother- 
nuclei, first into two, and then into four. The spores of this hybrid fern are 
always abortive. 
The above enumerated hybrids have parents possessing unequal 
numbers of chromosomes. There are other cases in which the parents 
possess the same number as in the case of P. kewensis (type). It has been 
shown that this hybrid, derived directly from P. floribunda crossed with 
P. verticillata , is sterile. On the other hand, Cannon ( 3 ) crossed two peas, 
both of which had 14 ( 2 x) and 7 {x) chromosomes, and the hybrid which 
repeated the same number was fertile. 
In certain 4 race hybrids ’ of Lathyrus odoratus, Gregory ( 23 ) found that 
abortion took place at various stages in the course of the meiotic division. 
The chromosomes were more ragged than were those of the parents and 
showed a deficiency of chromatin. Sterility in this ease is a recessive 
character and is generally confined to those plants which have light-coloured 
leaf axils, that being a recessive character. 
Finally, there are those cases of hybrids in which the chromosomes of 
the parents are too numerous, and the spindles of the hybrids too irregular 
to afford accurate data as to the relative numbers of the chromosomes. 
Such is the case with the hybrid Syringa rothomagensis , a cross between 
S. vulgaris and S.persica. Juel( 28 ) was unable to count the chromosomes, 
but he believes that there are more in the hybrid than in the parents. He 
finds very irregular spindles, and also the curious modification of amitosis. 
* Bei so vielen Arten von Unregelmassigkeiten bei der Tetradentheilung kann 
es nicht Wunder nehmen, dass S', rothomagensis in Bezug auf den Bliiten- 
staub fast steril ist ’ (p. 647). Tischler ( 39 ) has confirmed Juel’s investigation 
