1. Transmissibility of chromosomal aberrations induced in a nuclear reactor.

A study is in progress concerning the effects of irradiating maize pollen in a nuclear reactor on chromosomal aberrations transmissible through the male gametophyte. The work is being done at the California Institute of Technology in cooperation with Dr. A. E. Longley and Dr. E. G. Anderson and is made possible by a Johnson faculty fellowship from the University of Nebraska.

Crosses were made in 1947 between untreated female plants and male plants of which the tassels had been irradiated in a nuclear reactor. In 1948 the F₁ plants with abnormal pollen were outcrossed as males to one of the following good pachytene spreaders: L289 x I205, L289, or I205. In 1949 at least ten seeds of each outcross were planted at Pasadena and the resulting plants sampled for sporocytes and pollen.

The observations on pollen sterility are recorded in table 1. Only progenies in which at least two plants showed pollen sterility of ten per cent or more were included in the counts of the segregating progenies.

A cytological study of the chromosomal aberrations is in progress.

Table 1. Number and percentage of progenies of F₁ plants
with abnomal pollen outcrossed to normal plants,
segregating for pollen sterility of 10% or more.

Time of tassel exposure in nuclear reactor	Total number progenies	Number segregating progenies	Per cent segregating progenies
None	9	2	22.2
1 minute	55	24	43.6
2 minutes	98	44	44.9
4 minutes	84	44	52.4
8 minutes	27	10	37.0

Rosalind Morris