the only functional gametes of F; plants were unreduced, 
and repeated backcrossing to corn produced progenies 
which segregated for 2n and 2n+1 classes. The extra 
chromosome of the 2n+1 plants no doubt was derived 
originally from Tripsacum, and the two genoms of both 
classes of plants were originally corn chromosomes. In 
pachytene and diakinesis of the 2n+1 plants, the extra 
chromosome synapsed in low frequency with one of the 
pairs of corn chromosomes, forming a trisome. In other 
plants where several Tripsacum chromosomes were pres- 
ent, weak synapsis occurred between additional corn and 
Tripsacum chromosomes. Genetical results showed that 
an allele of sz1, not completely dominant to su; of corn, 
was transferred from Tripsacum to corn chromosome 4. 
In vegetative characters, the 2n+1 plants were so differ- 
ent from their 2n sibs that the two classes could usually 
be distinguished at a glance. The presence of a single 
Tripsacum chromosome resulted in partial sterility, both 
male and female.’ 
The work of Maguire (21, 22) confirmed the salient 
cytogenetical features reviewed above, except that in her 
stocks one extra Tripsacum chromosome produced only 
a negligible effect on the corn phenotype and no reduc- 
tion in ear fertility. In light of the possibility that the 
forms of 'Tripsacum with 36 somatic chromosomes might 
actually be tetraploids, as Farquharson’s (13) work 
strongly indicates, the results obtained by Maguire, and 
especially an interpretation placed on them by Randolph, 
are in need of review. 
Maguire’s cytological material consisted of seven 
stocks, which she stated were possibly distinct in the 
‘In an earlier publication (26), we attempted to estimate the num- 
ber of ‘T'ripsacum chromosomes present from the degree of pollen 
sterility. We have since become convinced from Maguire’s studies, 
as well as our own, that this method has little, if any, value. 
[ 861 | 
