Knowing from the progenies of some of the plants 
listed in Table V that the classification for J has been 
inaccurate in some cases, we have made another calcula- 
tion excluding J as one of the markers. The observed 
ratio of marked and unmarked chromosomes is now 100: 
63 and the theoretical ratio is 109:54. Chi-square for 
this ratio is 2.24 which represents a P value of 0.14. 
The closeness of the fit between the theoretical and 
observed ratios of marked and unmarked ‘Tripsacum 
chromosomes in this population is regarded as good, in- 
deed almost conclusive, evidence that Tripsacum con- 
tains two distinct genoms. One of these is so remotely 
related to maize that it contains no dominant counter- 
parts of the maize marker recessives tested so far and 
presumably its nine chromosomes are not homeologs of 
maize chromosomes. ‘This is the genom which we assume 
to have been derived from a genus of the tribe Andro- 
pogoneae, probably Manisuris. We are, accordingly, 
designating this the ‘‘manisuroid’” or X genom. The 
other genom is much more closely related to the maize 
genom, since it does carry dominant alleles of the maize 
recessive. Furthermore, some of these chromosomes have 
a similar gene content to their maize homeologs. For ex- 
ample, Maguire (1962) has found that the genes Wss, 
Lg, Glo which in maize occur on the short arm of 
chromosome 2, are also linked together on the long arm 
of one of the T'ripsacum chromosomes, although accord- 
ing to our recent unpublished data, the /’4 gene on the 
other arm of maize chromosome 2 is located elsewhere in 
our ‘‘Bussey clone” of 7°. dactyloides (2n of Kansas). 
Maguire (1961) found also that this Tripsacum chromo- 
some segment competes successfully about 5 per cent of 
the time in synapsis with maize chromosome 2 to the 
exclusion of its partner. Furthermore, she found that 
pollen bearing this extra chromosome from Tripsacum 
[ 306 | 
