Plant Reproduction
An essential requirement of agriculture is to understand how plants grow and reproduce.The earliest practitioners of crop production some ten thousand years ago had to learn to plant seeds and to keep them alive through watering and cultivation. Man eventually invented tools and machines that made farming more efficient and learned about plants themselves, leading to the development of crops that were of greater human benefit. The science of botany evolved from humankind's desire to know how plants live and reproduce. Their reproduction systems are functionally similar to those of animals. Most plants grown for agriculture have their sexual organs in their flowers. Whether the plants cross-pollinate or self-pollinate, it is essential that fertilization takes place for the production of seeds.
In the 1500s, German botanist Valerius Cordus (1515-1544) used the word pollen, Latin for powder or fine flour, to describe flower dust. In 1592, a Venetian named Prospero Alpini (1553-1616 or 1617) studied Egyptian flora while serving as physician to his government's consul in Cairo and published observations on the fertilization of date palms. He also disproved classical plant correlations. In the 1600s, an Englishman, John Ray (1627-1705), attempted a grand systematic description of all known plants and animals. Out of this came, in 1660, a three-volume work that listed and classified the plants in the area surrounding Cambridge. That effort was significant in that it sought to organize plants along lines of similarity and discussed, for the first time, sexuality among plants. Another Englishman, Nehemiah Grew (1641-1712), wrote in 1682 of the possibility of plant sexuality, suspecting that the parts of the flower played separate roles in plant reproduction. Rudolph Camerarius (1665-1721), a German botanist, conducted extensive research at the Botanic Garden in his home town of Tubingen. In 1694, he noted that the flower anthers, the pollen-bearing parts of the stamen, were the plant's male organs, while the style and stigma were the female organs. He not only confirmed what Ray, Grew, and others had suspected earlier, but also described the pollination process.
English botanist Stephen Hales (1677-1761) applied his interest in both plants and animals to describe the similarities in their circulation systems: that sap is to a tree what blood is to a horse or dog. His experiments led him to recognize plants' ability to absorb water and air and the importance of light in their growth. He summarized his conclusions in his book Vegetable Staticks (1727). The German botanist Joseph Gottlieb Koelreuter (1733-1806) published accounts of his research on plant pollen during a five-year period beginning in 1761. His successful cross-pollination of tobacco plants was his effort to prove the conclusions that Camerarius had reached earlier. Koelreuter also noted the uniformity and sterility of most hybrid plants, and observed the roles of nectar, wind, and insects in the transmittal of plant pollen. He is considered the father of plant hybridization. Another German botanist, Christian Konrad Sprengel (1750-1816), began research in 1787 on the pollination of geraniums, publishing his findings in 1793. He went further than Koelreuter by describing in greater detail flower structures and the role of insects. He discovered that the ability of some flowers to self-pollinate was attributable to the different maturation times of the anther and stigma.
German botanist Wilhelm Hofmeister (1824-1877) studied simple plants such as ferns and mosses in the late 1800s, discovering that these plants alternated generations, sexually reproducing in one generation while reproducing asexually in the next. He looked at plant cell division in microscopic detail and observed that plant ovules developed into embryos. He seems to have come close to discovering chromosomes in plant cells and is considered the father of modern botany. Gregor Mendel's discoveries of chromosomes and the laws of heredity in the late 1800s and the practical application of plant cross breeding by Luther Burbank in the early 1900s led to a new era in agriculture. For the first time in the long history of farming, agronomists could directly manipulate the reproduction of their crops. Plant breeding became an important part of mass crop production during the twentieth century. Further discoveries of gene structure--in particular the discovery of DNA (deoxyribonucleic acid)--has opened a new branch of agricultural research called genetic engineering.
Scientists hope that crop quality, quantity, and consistency can be achieved in the laboratory by altering gene structures and through the use of cloning techniques. Although much progress has been made in these areas of research, many individuals and groups voice concerns about the environmental impact and the effect on food safety of these processes. As man becomes more deeply involved with reproductive processes, utmost care must be taken to prevent environmental catastrophes that could affect both man and nature.
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