9. Viviparous mutants.


Work has been progressing on a series of viviparous (premature geminating) mutants. These mutants can be grouped into three general classes with regard to the color of the endosperm and of the seedling:


a.    With yellow endosperm and green seedling. Eleven mutants of this class have been grown, including vp1 and vp4. One of these mutants has been located in the long arm of chromosome one by means of a test with translocation B‑1a. Heterozygous viviparous plants pollinated by TB‑1a pollen gave some seeds with large endosperms (hyperploids endosperm and deficient embryo) which were viviparous, and also some seeds with small endosperms (deficient endosperm and hyperploids embryo) which were dormant. Thus this viviparous resembles vp5 in that dormancy in both of these mutants is determined by the embryo.


b.    With pale yellow to white endosperm and albino seedling. Three   mutants

      of this class have been grown. One of them (furnished by Dr. Sprague) has proven to be the same as vp5, which is located on the short arm of chromosome one. The third mutant is non­-allelic to vp5 and as yet has not been located.


c.    With pink endosperm and albino seedling. Eight of these have been studied and all have proven to be identical with one which was furnished by Dr. Sprague. As yet the location of this mutant is unknown.


In conjunction with these studies corn embryos which have obtained a length of one mm. or greater (about 14 days after pollination) have been cultured on sterile nutrient media. On transferring to culture conditions these embryos proceed to grow at once into seedlings. This indicates that there is something missing under culture conditions which are responsible for maintaining dormancy in their natural environment. An attempt is being made to determine the cause of maintenance of dormancy in normal seed development.


D. S. Robertson