Comparisons have been made at different developmental stages of the amounts of ribosomal RNA (rRNA) and of DNA in the cotyledons of two varieties of peas having different seed sizes. That with large seed has more rRNA per cell. The nature of the control of rRNA has been examined by the use of reciprocal crosses between the varieties. rRNA contents in the cells of a seed are not primarily dependent on the amounts of rDNA in those cells, but are regulated by the maternal parent; two hypotheses of the nature of this control are considered.
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