The Inflorescences of Maize

Abstract

1) The development of the maize plant, from germination to the maturation of the seed, is divided into the vegetative, transitional, reproductive, and seed stages. The ear and tassel differentiate and develop in the reproductive stage. 2) The mature tassel is a terminal, staminate inflorescence consisting of a symmetrical, many-rowed central axis and asymmetrical, two-ranked lateral branches. Paired spikelets, one terminal (pedicellate) and the other lateral (sessile), each containing two functional staminate flowers, are borne on the central axis and the lateral branches. 3) In contrast with the tassel, the ear is a pistillate inflorescence produced on a lateral branch. The ear consists of a symmetrical, many-rowed axis on which are paired spikelets, each containing two flowers. In the mature ear, it is difficult to distinguish the pedicellate from the sessile spikelet. There are two pistillate flowers in each spikelet of the ear, but only the terminal flower is functional, while the lateral flower aborts. 4) The mature ear and tassel appear to be different kinds of inflorescences, but if they are examined at the earliest stages in their development they will be found to be basically alike. The differences in the appearance of the two inflorescences at maturity are the result of differences in the differentiating and development of their parts. 5) Each of the morphological characteristics found in the maize inflorescences, except one, is present in other grasses, but the collection of morphological characteristics found in the ear and tassel is unique. One morphological characteristic not found in other grasses but found in the maize ear is the presence of a terminal, fertile, and aborted, lateral flower in each of the paired spikelets. 6) Axillary shoots are produced in acropetal succession in the axil of each leaf. Some of the axillary shoots that are produced at the beginning of the development of the plant may develop as tillers (suckers). The last-produced axillary shoot (or shoots) that is far enough advanced in its development at the initiation of the tassel develops into the ear (or ears). 7) The amount of seed produced per ear is determined by the number of rows of kernels and the number of kernels per row. The number of rows of kernels is determined at the beginning of the initiation of the ear, but the number of kernels per row may vary with the strain and with changes in the environment. Under comparable condition, seed produced per ear is less in plants without tillers than in plants with tillers. The average seed yield per ear is less in multiple-eared types than single-eared types growing under similar conditions. 8) The three major parts of the maize kernel are endosperm, 82 percent; germ, 11 percent; pericarp, seed coats, and tip cap, 7 percent. The composition of the maize kernel is 83 percent carbohydrate, 10 to 11 precent protein, and 4.3 percent oil. Fifty generations of selection for high- and low-protein strains and high- and low-oil strains produced marked changes in the chemical composition of the maize kernel. Beginning with 4.7 percent oil, after 50 generations of selection, the high-oil strain has 15.36 percent and the low-oil strain has 1.01 percent of oil. The protein content was 10.92 percent at the beginning of the selection and reached 19.45 percent in the high-protein strain and 4.91 percent in the low-protein strain after 50 generations of selection. Recovered inbred lines from backcrosses to the high strains have resulted in good-yielding hybrids that produce more protein or oil per acre than standard hybrids. 9) Several factors contribute to the superiority of maize over other cereals as a seed producer. The maize plant is large and, concomitant with its size, it has a large leaf surface, large stem, large root system, and an extensive vascular system. Branching is restricted to a few lateral, pistillate branches in which vegetative development is suppressed. The lateral ear-producing branch (or branches) is so placed on the plant that there are many leaves above and below it. The ear is large in diameter and has seeds that are many times larger than those of other cereals. All the afore-mentioned characteristics, many of which are not present in other grasses, contribute to making the maize plant a superior seed producer.