of which showed 10 maize bivalents and 18 Tripsacum 
univalents consistently. In the other, out of 84 cells 
examined, at metaphase, 27 (or 79.4% ) showed two tri- 
valents each, nine (or 26.5% ) showed one trivalent each, 
and 24 or 70.6%) showed an additional Tripsacum biva- 
lent besides the 10 maize bivalents. She attributed the 
trivalents to maize-Tripsacum exchanges in the Fy hy- 
brid, while the extra Tripsacum bivalent was assumed 
to have arisen from interchanges within the Tripsacum 
genom. ‘Thus, Maguire’s data, like ours, show a rather 
low intragenomic exchange either in the Fy or the trip- 
loid hybrid. In the one hybrid in which prior exchange 
is reflected it seems that maize-Tripsacum exchanges are 
more frequent than 'Tripsacum-Tripsacum exchanges. 
The foregoing data and discussion clearly demonstrate 
three facts: (1) there is low intragenomic paring within 
haploid maize, (2) there is also low intragenomic pairing 
within the haploid genom of ‘Tripsacum, and (8) pairing 
in the maize-Tripsacum hybrid is allosyndetic. 
If this allosyndetic synapsis involves all of the Tripsa- 
cum chromosomes such that the entire Tripsacum genom 
shows synaptic affinities to the maize genom, then one 
would assume that Tripsacum is a polyploid with two 
similar sets of chromosomes. In such a case, the chances 
for the members of a given Tripsacum genom to pair and 
exchange segments with their homologs or homeologs in 
the maize genom would be equal to their chances of pair- 
ing with the members of the second 'Tripsacum genom. 
This would be reflected as a higher (than observed) fre- 
quency of extra bivalents from Tripsacum in the triploid 
hybrid. Furthermore, in the Fy hybrid there would be 
at least some proportion of trivalent pairing. Since no 
such trivalents were encountered in the Fy hybrid of this 
test, the evidence indicates that the two genoms of 'Trip- 
sacum are dissimilar. 
[ 310 | 
