WEEDS OF NEW ZEALAND

Evening Post, Volume CXII, Issue 117, 13 November 1926, Page 21

WEEDS OF NEW ZEALAND

A PRESENT FBOM THE OUTSIDE

WORLD,

"Weeds of New Zealand," by F. W. . Hilgendorf, M.A., D.Se., P.N.Z. Inst. New Zealand: Messrs. Whitcombe and Tombs.

"A weed is a plant growing where it is not wanted. 'Weed' is a relative term —relative to man's desires. No plant is a weed." This .piece of philosophy—something similar has been said of human weeds —introduces Dr. Hilgendorf's informative little book. Twitches are weeds, yet they arc pasture in certain localities; so are sorrel and cats-ear. Even wheat is a weed when it grows in an oat crop. "The plant that will grow with most profit to man ih any given position is never a weed, but on the other hand anything but the best is a weed; thus, while Chewing's fescue and browntop. arc not weedsNm poor land, even ryegrass and cocksfoot may bo weeds on rich alluvial flats where timothy and foxtail would give more profitable returns."

The great majority of Now Zealand waeds come from England. Chcesemau's Hat gives 576 introduced plants, most of which are weeds of a greater or less degree of; importance.' From the North Temperate Zone come 463 of the 57C; 8(5 come, from the Tropics and the Southern Continents, and 28 from Australia. The native plants that function as weeds are not more than a score in number, ancl most^of these —p.g., fern and piri piri—arc weeds only on land that is not yet completely brought under cultivation. This book describes -31 introduced and 11 native

species.-' Acclimatisation in a new country sometimes brings extraordinary development to introduced animals or fish (example, trout), and something similar may occur in plant life, with a prospect of ultimate reaction. . This is how Dr. Hilgendorf puts it: "There are many instances of weeds being much more troublesome here than in their native country. Some sixty years ago Scotch thistle was iv this position, ana the settlers of those days feared that the country would be completely overrun by it. But the virulence of the attack passed, and Scotch thistle is now no more troublesome here than it is at Home. ' Foxglove is in similar case, and even Oalifornian thistle seems tobe going through the same phases, and to be much less aggressive now than it was ton years ago, It will probably in many localities reach the stage where it is regarded as a nuisance, but an avoidable one, and a system of farming will be adopted that will prevent the thistle being too troublesome." The name '' Calif ornian thistle "is misleading because'it disguises the fact that the.thistle is the very commonest of English pasture weeds, and the farmers in England make no particular outcry about it; "The passing away of the pristine vigour of an introduced weed is doubtless connected with the fact that every plant secretes into the soil something inimical to its own growoth—a**toxin, in fact, that inhibits its development. That soil toxins have any bearing on crop rotation may be doubtful, but the proved toxic effects on the soil as long as a plant is growing in it are more than enough to explain the loss of rigour of many introduced weeds."

Are the waxing and waning of tho trout in some districts, and of tho rabbit, in some districts, similarly explainable?.