1. In the preceding News Letter it was reported that tetraploid hybrids of Tripsacum and maize had been produced from experimental autotetraploids of maize pollinated by a natural autotetraploid Tripsacum from the Eastern United States. Repeated attempts to obtain seed from these hybrids by backcrossing to the parents failed. Since they produced only aborted pollen, with the possible exception of a very few grains partly filled with reserve food material, extensive attempts to self or sib cross these hybrids were not made. But very recently it was noted that a few partly developed seeds had formed on two of the 13 hybrid plants being wintered over in the greenhouse. These seeds apparently resulted from sib-crossing. By culturing the embryos of these seeds four seedlings have been obtained from which it may be possible to procure additional progenies.
During 1945 an initial attempt was made to repeat the cross of diploid corn and diploid Tripsacum made by Mangelsdorf and Reeves in 1930. A diploid Tripsacum from Kansas was used rather than the Texas form used by Mangelsdorf and Reeves. Very little difficulty was experienced in making the cross; 35 hybrids each with 28 somatic chromosomes were produced by pollinating 56 ear shoots of corn. The comparable frequency obtained by Mangelsdorf and Reeves was 29 hybrids from 382 ears.
Sporocyte examination of these hybrids is now in progress. The observations to date indicate that there is an appreciable amount of loose pairing at pachytene. Associations of 2, and not infrequently 3 chromosomes are prevalent at diakinesis. However, very few chiasmata apparently are formed as configurations suggesting chiasmata are rare at diakinesis and very few bivalent or trivalent associations persist to the metaphase stage. About one third of the figures have no bivalents on the metaphase plate and most of the other cells have not more than one or two bivalents at this stage.
The meiotic behavior of the chromosomes in these diploid Tripsacum-maize hybrids indicates that there has been very little if any exchange of parts of chromosomes during the meiotic prophase. The functioning of any mechanism for the transfer of Tripsacum chromatin to corn is conspicuous by its absence. It is quite possible that an occasional exchange of parts between the Tripsacum and corn chromosomes may take place as a result of something approaching typical crossing over, or fortuitous translocations; but it would be extremely difficult, on the basis of the observed cytological behavior of the chromosome in these hybrids, to account for a transfer of complete sets of knobs from Tripsacum to corn, as postulated by Mangelsdorf and Reeves.
However, the inference to be drawn from the observed meiotic behavior of the chromosomes in the F1 Tripsacum-corn hybrids, namely, that there has been little or no exchange of parts between the corn and Tripsacum chromosomes is in full agreement with the observation of Mangelsdorf and Reeves that the plants with no Tripsacum chromosomes in the progeny of triploid Zea-Tripsacum hybrids backcrossed to corn, "were for the most part, normal corn plants differing in no way from ordinary corn plants--most of the Zea chromosomes segregated out intact and completely uncontaminated by their association with those of Tripsacum". (M. and R., 1939, pp. 142-143).