The fourth point, which is concerned with how your neighbour has planted his land, also relates to your profits: because if he has an oak forest near your boundary, you cannot profitably plant olives in that vicinity, for the oak is so perverse in its effect upon the olive that not only will your trees bear less but they will even avoid the oaks and bend away from them until they are prostrate on the ground, as the vine is wont to do when planted near vegetables. Like the oak, a grove of thickly planted full grown walnut trees renders sterile all the surrounding land. 2° CONCERNING THE EQUIPMENT OF A FARM XVII. I have spoken of the four points of husbandry which relate to the land to be cultivated and also of those other four points which have to do with the outside relations of that land: now I will speak of those things which pertain to the cultivation of the land. Some divide this subject into two parts, men and those assistants to men without which agriculture cannot be carried on. Others divide it into three parts, the instruments of agriculture which are articulate, inarticulate and mute: the articulate being the servants,[73] the inarticulate the draught animals, and the mute being the wagons and other such implements. _Of agricultural labourers_ All men carry on agriculture by means of slaves or freemen or both. The freemen who cultivate the land do so either on their own account, as do many poor people with the aid of their own children, or for wages,[74] as when the heaviest farm operations, like the vintage and the harvest, are accomplished with the aid of hired freemen: in which class may be included those bond servants whom our ancestors called _obaerati_, a class which may still be found in Asia, in Egypt and in Illyricum. With respect to the use of freemen in agriculture, my own opinion is that it is more profitable to use hired hands than one's own slaves in cultivating unhealthy lands, and, even where the country is salubrious, they are to be preferred for the heaviest kind of farm work, such as harvesting and storing grapes and corn. Cassius has this to say on the subject: 'Select for farm hands those who are fitted for heavy labour, who are not less than twenty-two years of age and have some aptitude for agriculture, which can be ascertained by trying them on several tasks and by enquiring as to what they did for their former master.' Slaves should be neither timid nor overconfident. The foreman should have some little education, a good disposition and economical habits, and it is better that they should be some what older than the hands, for then they will be listened to with more respect than if they were boys. It is most important to choose as foremen those who are experienced in agricultural work, for they should not merely give orders but lend a hand at the work, so that the labourers may learn by imitation and may also appreciate that it is greater knowledge and skill which entitles the foreman to command.