TECHNOLOGY OF CEREALS FIG 2. 12 Radial section of a maize cob, showing(i) a perfect (fertile)and (ii a rudimentary(empty) floret. Based Nevertheless the quality of the grain is dependent e condition of the plant; diseases that affect the leaves, roots and stem can reduce the photosynthetic area, the ability of the plant to take up water and nutrients from the soil, and the ability of the plant to stand. Agricultural scientists have through experimentation, determined the optimal imes for field treatments such as fertilizer, herbi- cide and pesticide applications. For communicating this information it has been found convenient to FIG 2. 13 Cob of maize, showing the protective husk define stages of plant growth and several scales have been devized. Those that exist for wheat, the same foret. Once on the stigma, pollen grains barley and oats have been compared by Landes have a mechanism whereby a pollen tube is and Porter(1989). The decimal scale of Zadoks produced. The tube progresses towards the micro- et al.(1974)is illustrated here(Fig. 2. 14). pyle and having effected access by this route, it Scales usually start at the time of seed germina- allows nuclei from the pollen grain to pass into tion but a life cycle is, by definition, a continuously the ovule and fuse with nuclei present there. The repeating sequence of events and, as such, has no primary fusion is of the sperm nucleus with the absolute beginning or end egg nucleus. The product is a cell, the e successive The beginning of each new generation occurs divisions of which produce the embryo. A further when pollination is effected. As in all plants this set of fusions, however, produces the first endo- results when pollen produced in the anther con- sperm nucleus. Three, not two, nuclei are involved tacts the stigma on the carpel of another, or even one from the pollen and two polar nuclei from the34 TECHNOLOGY OF CEREALS FIG 2.12 Radial section of a maize cob, showing (i) a perfect (fertile) and (ii) a rudimentary (empty) floret. Based on A. L. and K. B. Winton (1932). Nevertheless the quality of the grain is dependent upon the condition of the plant; diseases that affect the leaves, roots and stem can reduce the photosynthetic area, the ability of the plant to take up water and nutrients from the soil, and the ability of the plant to stand. Agricultural scientists have, through experimentation, determined the optimal times for field treatments such as fertilizer, herbi￾cide and pesticide applications. For communicating this information it has been found convenient to define stages of plant growth and several scales have been devized. Those that exist for wheat, barley and oats have been compared by Landes and Porter (1989). The decimal scale of Zadoks et al. (1974) is illustrated here (Fig. 2.14). Scales usually start at the time of seed germina￾tion but a life cycle is, by definition, a continuously repeating sequence of events and, as such, has no absolute beginning or end. The beginning of each new generation occurs when pollination is effected. As in all plants this results when pollen produced in the anther con￾tacts the stigma on the carpel of another, or even FIG 2.13 Cob of maize, showing the protective husk. the same floret. Once on the stigma, pollen grains have a mechanism whereby a pollen tube is produced. The tube progresses towards the micro￾pyle and, having effected access by this route, it allows nuclei from the pollen grain to pass into the ovule and fuse with nuclei present there. The primary fusion is of the sperm nucleus with the egg nucleus. The product is a cell, the successive divisions of which produce the embryo. A further set of fusions, however, produces the first endo￾sperm nucleus. Three, not two, nuclei are involved, one from the pollen and two polar nuclei from the