26/46 The water-cress (Nasturtium officinale) grows with amazing vigour in many of the rivers, forming stems 12 feet long and 3/4 inch in diameter, and completely choking them up. It cost L300 a year to keep the Avon at Christchurch free from it. It forms a dense mat, exterminating other plants, and preventing cultivation. It can, however, be itself exterminated by sowing the ground with red clover, which will also vanquish the Polygonum aviculare. The most noxious weed in New Zealand appears, however, to be the Hypochaeris radicata, a coarse yellow-flowered composite not uncommon in our meadows and waste places. |