The cultivation of plants, like the domestication of animals, must undoubtedly have had some accidental beginnings in the camping places of primitive man. Seeds and roots from vegetable spoil which he had gathered and brought home must often, under favourable conditions, have been seen to germinate and sprout; there may sometimes have been a return to see what might have sprung up, as if by magic, at some former camping site. But the systematic cultivation of the soil depended upon an awareness of the processes of nature and their seasons and the choice of a suitable area, such as nature provided in the great river valleys of the Near East, for a more or less deliberate act of social experiment. The result was the securing, save in bad seasons, of a far bigger surplus food-supply than man the food-gatherer or tentative domesticator of animals could have dreamed of--the food-supply which launched the Neolithic revolution.

Agriculture in its simplest forms involves the clearing and breaking-up of not too arid surface soil; the sowing and covering of the seed; destruction of weeds and the conservation or application of water during the growth of the crop; and, after harvesting, the safe storage of the crop and the setting aside of seed for the next season. Virgin soil might be found and used for each crop--the practice known as 'extensive' agriculture--but as soon as it became necessary, or convenient, to till the same ground year after year, deeper cultivation was required to delay exhaustion. Hence the fundamental invention of the plough, though its full development came when men had to wrestle with the heavy soils of northern Europe. In Mesopotamia and Egypt the most important problem was that of supplying the soil with water.

Though tillage and irrigation were arts in which man developed his new technical skill, what had to come first was the choice of plants on which to practice them. A list of those used in prehistoric Europe is astonishingly varied, including industrial as well as food plants, and among the latter are a good many varieties that are nowadays ignored. Green and root vegetables are too perishable to leave many traces in the archaeological record, but their quick growth makes it tolerably certain that they were cultivated early. Fruit, which takes several seasons to become established, is likely to have been cultivated rather late, but evidence of figs, apples, pears, and small plums is to be found at late-Neolithic sites in Europe. Nuts had certainly been important as a gathered food from the very earliest days: the walnut was brought into northern Europe from southern climates such as that of Greece, where it was first cultivated on a large scale. In the hazel-nut we have an example of a tree of which the fruit has been eaten since Mesolithic times at latest, but which has even now barely entered the stage of cultivation. With nuts may be grouped the oil-bearing seeds, ranging from those of flax and the opium poppy and the sesame of ancient Mesopotamia to the olive tree, which spread from the eastern shores of the Mediterranean to make its home also in Greece, Italy, the south of France, and Spain. The cultivation of oil-producing plants became especially important because it provided mankind with a far larger supply of oils and fats --indispensable as a foodstuff and highly valuable also for certain industries and as an illuminant--than could possibly be produced through the domestication of animals.

There remain the two great stand-bys of man's larder, the pulses and the cereals. Both crops are easy to cultivate and easy to store; if the spread of the pulses may be connected with the fact that this is of all the crop-plants the one with the largest number of species, the cereals present a picture of few species very widely distributed. Beans, peas, and lentils have all been cultivated in Europe from Neolithic times, and pulses, particularly in the form of the soy bean, continue to provide the main protein food for whole populations in the East today. But cereals have become the most important crop of all, and it is therefore of interest that a primitive type of wheat and two-row barley are both found at one of the earliest agricultural sites--Jarmo, in north-eastern Iraq--in a Neolithic deposit dated at about 5000 B.C. The six-row type of barley came later, from the Far East, but both forms of barley entered Europe together, along with primitive types of wheat. Rye, a common weed of the wheat field, largely took the place of wheat in the north when a worsening of the climate at the end of the Bronze Age drove the wheat southwards. Weed is a relative term, however: the stomach contents of an Iron Age man, whose body was preserved in a Danish bog for 2,000 years, show that he had eaten at least a dozen of our commoner weeds, some of which were once cultivated and all of which may well have served to make his cereal porridge less monotonous in taste and more nourishing in content. Oats are native to Europe, and in northern regions climatic conditions render them the most dependable cereal crop. This is a fundamental factor determining local patterns of agriculture, since farmers grew what experience had shown to be best suited to their particular soil and climate: other requirements were imported, as trade routes permitted, from regions more favorable to their production.

There is the same uncertain dividing-line between weeds and useful plants in the case of industrial crops. Flax, cultivated originally for its linseed oil, was being grown for textile use in both Mesopotamia and the Nile valley by about 3000 B.C. We think less readily of the part which the nettle played as a fiber plant, though in fact nettle-cloth was still being made in Europe at the time of the First World War.

Cultivation proceeded for a long time by trial and error, many kinds of crop and different methods of growing it being tried until the few best came very slowly to predominate. The establishment of regular crops produced the first big surplus; the surplus in turn gave rise to the specialist; the existence of the specialist to the specialization of agricultural tools.

There is a sense in which agricultural implements precede agriculture. Thus the reaping knife or sickle was developed originally for the cutting of wild grasses. In Mesopotamia it was made of baked clay; in Europe the most primitive form had handles made of antlers, grooved to take overlapping flint flakes; but the commonest form, as we might expect, had a short wooden handle holding either flint teeth or a single sharp piece of flint. Moreover, the ground and polished stone celts--the axes and adzes of flint and other stones that are characteristic of the Neolithic stage--had their place in a hunting economy as well as in an agricultural one. The improved axe, with which the farmer began his long task of clearing the European forests, must also have helped in the chase. The adze, which we think of as a wood-working tool, was used by early cultivators also as a hoe. . .