PLANTS AND MAN our green slaves

From the beginning of history man has had an economic interest in the plants which form part of his environment. This interest has been essential for his survival and subsequent development from the earliest civilizations to our present urbanized societies. About 10,000 years ago agriculture was born; man learned to recognize specific plants and animals as being particularly valuable and started, albeit in a rather primitive way, to encourage their growth by planting, feeding and protecting them. In principle it was a short step from this to the more rigorously controlled plant and animal husbandry that is familiar to us today. As man’s knowledge of plants and plant products has increased so has their use and exploitation and there are hardly any aspects of any present-day society which have not been influenced in some way by the use (or occasionally misuse) of a plant product.

Plants as a source of food

Cereals and vegetables

Agriculture is dominated by man’s need for basic food-stuffs containing energy-giving carbohydrates and body-building proteins. Throughout the world vast quantities of cereals and vegetables are grown, both for direct utilization by man and also for animal feeds. No other group of food plants have been so important to mankind as the cereal grains. Cereals provide nutrition for more than two billion people and their production is in excess of one billion tons annually. Without the cereals, civilization as we know it would not exist. Fruits

Even after man had settled down into some sort of communal life based around a primitive agricultural system, searching out wild fruits and hunting for game was still an important part of his existence and contributed in no small way to his survival. Until quite recently fruit production remained a rather casual and local affair, but with improvements in freezing, canning, storage and transportation, the fruit industry has increased in size and importance. Now, fruit tends to be grown in large orchards and plantations which require complex equipment for the maintenance, harvesting and processing of the crop.

Botanically, fruits are the matured ovaries of angiosperms, but this distinction is not always clear to the layman. For example, nuts are fruits, or at least the seeds of fruits, but very often they are placed in a distinct group. The word fruit conjures up the picture of a fleshy, pleasant-tasting and juicy delicacy picked from a tree or bush and it is in this sense that they are considered here. Fruits exhibit a tremendous range in taste and nutritional value, from the watery pumpkin through firm and fleshy products such as apples and peaches to high-carbohydrate-containing dates. Many fruits however, contain little energy, but instead are very watery. Nevertheless many are good sources of minor minerals and vitamins and so form an essential part of our diet. Fruits can be divided into three main groups: fruits from herbaceous annuals; perennial fruits from temperate climates; and tropical fruits.

The first group includes tomatoes, peppers and aubergines (all members of the Solanaceae) and melons and squashes (members of the Cucurbitaceae). Some of these are commonly thought of as vegetables but are botanically true fruits. They are usually grown as summer annuals in temperate climates and so tend to be rather seasonal in availability.

Included in the perennial fruits from temperate climates are the so-called ‘stone fruits’ such as peaches, apricots, cherries and plums. The fruit is referred to as a drupe and consists of an outer skin (epicarp) containing the thick fleshy part we eat (mesocarp) which surrounds the stone (endocarp) containing a single seed. Apples and pears are also found in this group. They, are referred to as pome fruits and are really ‘false fruits’, the greater part of which is developed from the receptacle of the flower and not the ovary. For example, the part of the apple which we cat represents the receptacle, the core being the ovary. Also included are berries, which are many-seeded succulent fruits such as gooseberries and grapes, or aggregate fruits such as blackberries and strawberries. An enormous amount of investigation has been undertaken concerning the propagation, growing and handling of temperate-zone fruits and their economic utilization probably represents one of the most intensively mechanized parts of agriculture today.

A huge range of tropical fruits exists reflecting the wide diversity of tropical vegetation. With the exception of bananas, pineapples and citrus fruits, tropical fruits are not so widely cultivated as are those from temperate zones although some, such as avocadoes, mangoes and guavas are becoming more widely available with more rapid transportation methods. The majority of tropical fruits such as tamarinds, loquats and breadfruit, although widely distributed, are very often utilized only where they grow.

Sugars and starches

Sugars are the soluble forms of carbohydrate in plant cells and can be directly utilized for energy and growth. Starch is an insoluble form which is used for food storage.

Although there are many different sugars which occur naturally, only a few are extracted and used in any quantity, the most important one being sucrose (commonly known just as ‘sugar’) mainly obtained from sugar cane or sugar beet. Over 60 million tons of sucrose, initially obtained from plants as an expressed juice, are produced annually. Sucrose is used not only as an additive to other foods and drinks to make them more palatable but also for fermentation and as an industrial raw material.

The main growing areas of sugar cane in the Caribbean, South America, southern Asia and the Central Pacific account for something like three-fifths of the world’s total production of sucrose. Extraction of sucrose from sugar beet accounts for most of the rest of the world’s production of sugar. Sugar beet extraction was developed, mainly in Germany in the late eighteenth and early nineteenth centuries, in order to gain some degree of independence from tropical sources. The industry quickly expanded and today forms an important part of the agricultural productivity in all continents except Africa, the main producers being, north-em Europe, USSR and USA.

A less important source of sugar is the gathering of maple syrup from the sugar maple (Acer saccharum). This was first accomplished by the American Indians who hacked wounds in the maple trunks and collected the exuded sap in crude wooden or pottery vessels. Today, in the early spring, metal spiles (or spouts) are driven about 5cm (2in) into the trunks and the sap allowed to accumulate in a pail. Controlled evaporation of the collected sap then produces maple syrup, annual production of which amounts to several million litres.

Starch can be obtained from a wide variety of plants. Normally the starch-bearing cells are broken open and the abundant starch grains within floated free or separated by centrifugation. Commercially two sources have been exploited: the temperate <Zea mays (maize or corn) and the tropical Manihot esculcnta (manioc, cassava, tapioca, etc) although other sources such as potatoes, wheat, rice, arrowroot and sago are also used. Starches have an enormous number of uses and are encountered in modern economy almost everywhere. They are found in various foods, such as puddings, chewing gum, bakery products, in adhesives and pharmaceuticals, as textile stiffenings and paper coatings and, following hydrolysis, in a whole number of products from sweets to tobacco flavourings. Beverages

Man has always sought to make his drinks more palatable and more interesting to the taste than is pure water. An obvious alternative to plain water is fruit juice, either used as such, or fermented to make wine or cider. One step removed from this are the diffusions and decoc- tions from various processed plant parts, for example tea and coffee, which are so commonly used today.

Tea is obtained from the tea plant, Camellia sinensis, and is produced mainly in Southeast Asia. China, India and Sri Lanka being the prominent growers. The tea bush is a flowering shrub which grows best on a well-drained acid soil in a warm climate which has ample rainfall (150-50OCIT1 (6o-20oin) per year). The plants are usually heavily pruned and not allowed to reach more than I-I-sm (3~5ft) in height. Harvesting is usually done by hand to ensure the best quality tea and only the terminal two leaves (sometimes terminal three or four in poorer quality teas) are plucked.

The processing of the harvested leaves is quite complicated; for the black tea favoured in the West, the leaves have to be withered, rolled, fermented and fired, while for the green tea used mainly in the East a less elaborate procedure of drying and rolling is employed. The quality of the tea produced is dependent on a number of factors: care taken in cultivation, rainfall and elevation at which it was grown. The flavour is dependent on its content of essential oils and other soluble components, while its refreshing and stimulative properties are the result of its caffeine content which occurs in the leaf in concentrations of 2-5 percent.

Coffee is another beverage which depends upon caffeine for its stimulating properties. Coffee is obtained mainly from an Abyssinian shrub called Coffca arabica. This plant has glossy deep-green leaves and bears fragrant white flowers two or three times a year. The flowers give rise to two-seeded drupes (the coffee-berries), each tree producing something like 3kg (6-6lb) of berries per year.

One of two methods is used for processing following harvest. If water is scarce, the gathered berries are dried in the open and then stored in bins for later processing to obtain the seed following removal of the outer pericarp. In the alternative ‘wet’ process, which produces better quality coffee, the outer fleshy layers of the berries are removed by pulping machines. After thorough cleaning, the de-pulped fruits are further treated to obtain the familiar coffee beans ready for roasting. The roasting process is essential for the development of flavour, which is due to certain essential oils and caffeol. The process also helps break down the cell walls of the bean and facilitates the grinding process. The stimulant in coffee is caffeine which occurs in the beans to the extent of 1-2 percent.

Cocoa or cacao is made from the seeds (beans) of a small tropical tree originally found and cultivated in southern Mexico and the northern parts of South America. Long before Columbus’ visit it was a highly prized beverage in Mexico and Peru; now its cultivation has been vastly extended, with Ghana in Western Africa becoming the greatest centre of production. The cocoa tree {Theobroma cacao — ‘theobroma’ meaning ‘food of the gods’) grows as a many-branched tree with a maximum height of about 8m (26ft). The flowers are borne on the older branches and trunk from which develop large ellipsoid-shaped pods containing between 30 to 50 seeds or beans. The beans are rich in oil, protein and starch but the familiar chocolate taste is not found in the fresh material and must be developed by a process which involves fermentation. Spices and essential oils

Essential oils in the guise of perfumes and spices have been some of the most sought-after bot- anical products in the world. The search for spices and the resulting intensification of the spice trade influenced the course of history and encouraged the setting up of colonial rule, the repercussions of which we are still experiencing. The essential oils, responsible for the aroma of spices and the fragrance of flowers, are widely distributed throughout the plant kingdom. They are usually small molecules, typically liquids, possessing an aromatic fragrance which is easily detectable owing to their volatility in contact with air. They may be produced in different parts of the same plant, such as leaves, bark, roots or seeds, and are commonly secreted into special glands from which they can pass through the plant cuticle into the air. Essential oils are most often extracted from the solid portions of the plant tissue before their use in perfume products and food flavourings—they are also used as antiseptics, insecticides, solvents in the paint industry, components of glues, inks, polishes, etc. Most spices consist of the plant parts themselves and are ordinarily prepared by drying and grinding, such processing being carefully undertaken to prevent loss of the essential oils by volatilization.

Cinnamon is a very ancient spice obtained from the bark of Cinnanwnnim zeylanicum. The cinnamon tree is small and bushy with thick shiny leaves and rather inconspicuous flowers. The bark contains about 1 percent of a volatile oil, mainly cinnamic aldehyde, and is either used directly or extracted for the oil. The main production is from Sri Lanka and the Seychelles Islands but trees are also grown in southern India, China, Malaysia and Indonesia.

Clove trees (Eugenia caryophyllata) flourish best on well-drained soils in maritime climates with 220-250CIT1 (86-o8in) of rainfall annually. The main areas of production today are the Malagasy Republic and Indonesia. The cloves of commerce are the dried unopened flower buds from the trees, and when mature each tree may yield up to 35kg (wlb) of dry cloves per year. The deep rose-pink clusters of buds are harvested and then sun-dried on matting: they are then either marketed as such or distilled to produce clove oil which contains 80-95 percent eugenol.

Ginger comes from the sun-dried rhizomes (root-stock) of a tropical hejb, Zingiber officinale. The plant is widely grown in tropical countries but most of the world’s supply of ginger comes from India and Taiwan. The pieces of harvested rhizomes are prepared for market by peeling, washing and drying in the sun.

Yet another tropical tree species which acts as a source of spices is the nutmeg tree (Myristica fragrans). Nutmeg is cultivated principally in the West Indies, Indonesia and Sri Lanka. The tree bears fruits which are like orange-yellow plums. When ripe the fruit splits open to reveal a brilliant red membrane called an aril that surrounds the seed. When dried, this membrane fades to an orange-yellow colour and forms the well-known spice mace. When the seeds are dry they are removed from their shells for use as nutmeg.

Pepper, from the pepper plant (Piper nigrum), is the most important of all spices in terms of world trade. Peppercorns are the dried fruits of this clinging vine with shiny leaves and adventitious roots which enable it to cling to the trunks of trees. It is mainly produced in India and Indonesia but some also comes from Brazil and the Malagasy Republic. Black pepper is produced from the ripening berries which are picked soon after they turn from green to red. As they are dried the berries turn black, when they are ready for marketing. White pepper is produced by allowing the berries to ripen further and then removing the outer black skin by boiling or fermentation.

Spices from temperate regions perhaps seem more prosaic than those of the tropics, but nevertheless they make an important contribution to food flavourings in many parts of the world. Many of them belong to the family Umbelliferae (such as dill, anise, parsley and coriander) while another important group is the Labiatae (such as sage, mint and savory). Many of these herbs are grown on a kitchen-garden basis but limited growing of the more important ones is practised.

Peppermint (Mentha piperita) and spearmint (M. spicata) began to be important commercial crops in the early twentieth century. Usually the plants are machine-mowed and the mowings allowed to dry in the fields to reduce their moisture content. The crop is then collected and usually distilled to extract the essential oils, the most abundant constituent of peppermint oil being menthol while that from spearmint is carvonc. World production is largely centred in the USA, USSR and Japan, where a different variety of mint, M. arvensis (Japanese mint) is grown.

Sage (Salvia officinalis) is a many-branched plant with slender greyish leaves native to the Mediterranean area and Yugoslavia is the main centre of commercial production. The foliage is harvested when the plants begin to bloom, normally by mowing and raking. The dried leaves contain less than 2 percent of various essential oils and are used almost exclusively for food flavouring.

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