Miniature Seed-a Study in the Development of a Defective Caryopsis in Maize.

HE normal product of fertilization in maize is a mature dormant seed T with a well developed embryo and starchy endosperm. All the many variations from this norm have been in a minus direction with regard to embryo or endosperm development and must be regarded as defective types. These defective types may be divided superficially into two groups on the basis of comparison of their growth to that of plants of similar genetic constitution but carrying the normal allele of the gene in question. The first group would comprise those defectives in which the homozygous defective plants are approximately equal in vigor, size, and maturity to the normal, although they may be somewhat smaller in early growth stages. The second group would include all the lethals, semi-lethals, and stocks in which the factor in question finds expression throughout the sporophytic generation and makes the plants shorter, lighter in color, more slender, and generally less vigorous. Defectives of the first class are waxy, sugary, shrunken, and miniature germ. All these genes approach normal very closely in seed development as judged by weight. Waxy and sugary are products of upsets in carbohydrate metabolism-waxy corn forming exclusively amylopectin instead of a mixture of both amylose and amylopectin as in ordinary maize (SPRAGUE, BRIMHALL and HIXON 1g43), while sugary cannot synthesize glucose into maize starch (EAST and HAYES 1911). WENTZ (1924) reported that miniature germ with a very small embryo has low germination and is weak in early growth stages but recovers to make a normal, mature plant. The second group of defectives includes many genes, most of which form seeds with only two to 3 0 percent of normal development. Many workers ascribed such deficiency to faulty pollination or arrested development due to competition and dominance. However, JONES (1920) showed a heritable basis for some of these defects-stocks where development of the embryo and endosperm stopped completely shortly after fertilization. Since that time many deficiencies have been shown to be heritable. MANGELSDORP (1926) made a comprehensive study of 14 defective seed characters. These stocks ranged from those in which development was about 57 percent of that in normal seeds, and homozygous plants although stunted could be grown (dei'), to one where development is about three percent of normal and viability is nil (de14). MANGELSDORF found a good deal of correlation between endosperm and embryo development in all his stocks. There was no satisfactory development of one without the other. Other investigators have not always confirmed this in other defectives.