When it is required for food germination is permitted, but is soon stopped: the ants nibble off the growing rootlet of the seed. Then when the grain absorbs water and begins to change its starch into sugar, the ants suck in the sugar and reap the reward of all this labour and skill. In the conduct of this germination of the grain they are, of course, far in advance of all the savage races of mankind. There are certain South American species which go at least one step farther. They have their own fields--spaces three or four feet in diameter--which are entirely occupied by one single grass, the so-called Ant-rice (_Aristida stricta_). Dr. Lincecum states that the ants "work" these plantations very carefully, removing every weed or other plant that comes up, and sowing every year the new seed at the proper season.[129] [129] _Proceedings Linnean Society_, 1861. Dr. MacCook adds nothing essential, and in no way disproves Dr. Lincecum's statements. These facts are sufficiently strange and startling, but there are even, apparently, species still more intelligent, who not only sow and reap, but actually prepare a soil and reap a crop of mushrooms, or at least, if not of mushrooms, of fungi. These wonderful little insects gather leaves and cut them into fragments of an appropriate size; they are then collected together so as to form a bed, and the fungus is introduced to this. The fungus is kept at a certain stage of growth by very careful treatment; the fruit-bearing ends are nibbled off, so that the young shoots come up indefinitely. The ants feed upon these fungus shoots, and get a crop indefinitely prolonged. This is, of course, a system of agriculture far beyond that employed by any tribe of savages. Only man in a relatively advanced stage of agriculture grows mushrooms for himself. These facts, startling as they may seem, are apparently quite well authenticated and have not been seriously questioned. There are a great number of leaf-cutting ants who are, indeed, amongst the most dangerous of the many insect pests in South America and elsewhere. Wallace (_Revue Scientifique_, 179, p. 29), in speaking of the Saauba or leaf-cutters, describes how he placed a large heavy branch across the route of one of their columns. The long line of laden ants was checked, and the greatest confusion set in at the head of the column. Each ant, for several feet down the column, then laid down its leaf, and all set to work to tunnel under the obstacle. This was managed in about half an hour's time, and the column then proceeded on its way. Amongst other interesting and curious facts connected with these extraordinary insects is that some kinds are actually kept up by certain plants as a sort of standing army or police.