A WORLD-WANDERING PLANT.

Otago Witness, Issue 2757, 16 January 1907, Page 77

A WORLD-WANDERING PLANT.

By Dctobxis. Plants are great wanderers — everyone who knows anything about them knows that. Those who don't know it can easily convincfe themselves by a little exercise of the faculty of observation. Moreover, plants have among them an astonishing variety of ways of getting about in the world. Take the common dandelion, whose bright yellow disc is known to everybody, one might almost say everywhere. It is true that the individual dandelion sits still and rooted on the same spot for an indefinite number of years," so far as I know. But it was born of a roving seed itself,' and it begets multitudes of like kind every summer season. In these seeds of the dandelion we have a firio illustration of the simple means by t»j" of -which many plants in course of their evolution have managed to effectually solve the problem of aerial navigation. Oould anything be less complex than the delicate parachute which, crowns each ripe dandelion seed? Poised - gracefully ready, it sits waiting for the first favourable breeze which will carry it far from the maternal etem. It is, in fact,' one of those wonderful adaptations of which the world of living things exhibits an almost endless variety. Wherever we look we find them iv one form or another, and just as the dandelion 6eed finds itself wafted away to find a suitable spot whereon it may establish itself, so do other plants 6how powers of getting about with facility in search of fresh dwelling-places. A vast number of plants thus depend solely upon modifications of their seeds and the appendages of these, or upon peculiarities in the structure of the seedTessel, for purposes of migration. During any sunny day in summer we may hear the gorse pods exploding by the wayside, and every bursting pod scatters a few seeds to a distance, thus giving them a better chance of finding fresh ground in which to germinate and develop. Certain members of the geranium genus shoot their seeds to a considerable distance — 20ft or more, — and tie common balsam, or "fireman's helmet," effects a perfect fusilade in firing off the ripe contents of its pupa-like seed capsules. Other plants, as the familiar piri-piri, or "biddy-bid" ; sedges, burre, and many grasses, are furnished with harpoon-like barbs, miniature fishhooks, and other clinging devices, enabling them to get free carriage away from their immediate bbit:r t:u ~1~ 1 ' w ""' The plant figured here, which bears the well-sounding name of Anacharis alsinastrum, without using any such means of transportation, has got about the world to an extent that has rendered it a 6erious nuisance in many widely-sepa-rated countries. In its native home on the American continent, as I infer from a cursory inspection of the weed and its inflorescence, its seeds are carried by water. It could hardly be otherwise, indeed, for anacharis lives entirely submerged in ponds and slow-flowing rivers, only sending its tiny flowers to the surface to be pollinated, also by the agency of water. This water -weed, like many land plants, bears the staminate, or male flow- m v era, and the stigmatac, or female flowers, on separate individuals. Hence it follows that if the pollen-bearing members be absent there can be ra> production of fertile seeds In Britain, New Zealand, and other land 6 to which tins unpretending water- weed has made its way, this is just what happens. Only the female plant is present, the male being entirely unknown in tnese lands. It has been propagated entirely from chance fragments thrown into ships with ballast, or used as packing mayhap. In England this plant emigrant from America has been known since about the middle of the last century. It is believed to have come over with a cargo of logs, and thus gpt itself introduced to a new and congenial habitat. It was first observed iv a canal at Market Harboroufjh about the year 1847. Thence it has spread over England, and proven itself a costly thorn in the flash of water-con<-ervaiicy boards and other interested parties. Thousands of pounds are expended annually in tearing this noxious plant out of the beds of canals and slow-flowing rivers, and in many places it seriously impedes and even totally arrests navigation. It was found in a pond in Berwickshire five years before the date of its appearance in England, and now it would be difficult to mention a locality in the United Kingdom that is free from its unwelcome presence. From Britain it has made its way to New Zealand and other outlying portions of the Empire, and as stoutly refuses to be suppressed in one place as in another. Anacharis is quite common in and about Dunedin, and until recently the ponds in the Botanical Gardens used to be choked up with it. I have seen tons of it dragged out and thrown on the margin, . but that process only checks without repressing its luxuriance. However, since tjie swans were introduced at the ponds the weed has disappeared. Swans have been found similarly useful in email Srivate ponds in England for years past, ut for Mr Tajonock's devotion to barbed

wire and netting one might attempt to discover if the -need still grows in short lengths at the bottom. Piobably it does, and is continually cropped by the swans. In the Victoria Park pond and at "YVoodhaughthe weed is still in possession, forming submerged forests wherein multitudes of aquatic animals find congenial surroundings. The plant is interesting if for nothing other than its tramp-like habit of stealing a lift, an utterly passive thing, carried hither and thither by chance agencies, and proving itself unwelcome and a nuisance wherever it finds itself. I have found it useful in the making of fresh-water aquaria — it will grow in anything that holds water. — but beyond this small commendation it seems hardly possible to say a word in favour of this travelled and troublesome weed. If there is any moral to be deduced from its story, it would ecem t</ fc^s this : that n7a.n & dominion over Nature can only be maintained by constant warfare — even against insignificant weeds.