If, on the other hand, the true reading be '_ab universis in_,' or '_per, vices_' or '_invicem_,' the meaning probably is that fresh tracts of land (_agri_) are one after another taken possession of by the tribal community when it moves to a new district or requires more room as its numbers increase. The new _agri_, the passage goes on to say, are soon divided among the tribesmen or the _trevs_, '_secundum dignationem_,' according to the tribal rules, the great extent of the open country and absence of limits making the division easy, just as it was in the instance of Abraham and Lot. «The agriculture is a co-aration of fresh portions of the waste each year.» In any case it is impossible to suppose that Tacitus meant by the words _in vices_ or _invicem_, if he used them, that there was any _annual_ shifting of the tribe from one locality to another, for it is obvious that the very next words absolutely exclude the possibility of an annual movement such as that described by Cæsar. '_Arva per annos mutant et superest ager._' They change their _arva_ or ploughed land yearly, _i.e._, they plough up fresh portions of the _ager_ or grass land every year, and there is always plenty left over which has never been ploughed.[524] Nothing could describe more clearly what is mentioned in the Welsh triads as '_co-aration of the waste_.' The tribesmen have their scattered homesteads surrounded by the lesser homesteads of their 'servi.' And the latter join in the co-tillage of such part of the grass land as year by year is chosen for the corn crops, while the cattle wander over the rest. [p345] This seems to have been the simple form of the open field husbandry of the Germans of Tacitus. And this is sufficient for the present purpose; for whichever way this passage be read, it does not modify the force of the previous passages, which show how manorial were the lines upon which the German tribal system was moving even in this early and still tribal stage of its economic development, owing chiefly to the possession of serfs by the tribesmen. It gives us further a clear landmark as regards the use by the Germans of the open-field system of ploughing. Tacitus describes a husbandry in the stage of 'co-aration of the waste.' It has not yet developed into a fixed _three-course_ rotation of crops, pursued over and over again permanently on the same arable area, as in 'the three-field system' afterwards so prevalent in Germany and England. «The tendency of the German tribal system unlike the Welsh towards the manor.»