386 Tj-ansactions. — Botany. 



Art. XXX. — Notice of the Establishment cf Vallisneria spiralis 

 in Lake Takajnina, together with some Reviarks on its Life- 

 Ms tory. 



By T. F. Cheeseman, F.L.S. 



[Read before the Auckland Institute, 3rd August, 1896.] 



Nearly three years ago my friend Major Mair showed me an 

 aquatic plant which he had gathered in Lake Takapuna, and 

 which he rightly concluded to be a stranger to our flora. 

 When first seen it formed a dense mass of no great size in 

 comparatively deep water in front of his boathouse, and 

 several similar patches were noticed not far away, all being on 

 the southern side of the lake. None of the residents near the 

 lake knew the plant, and none of them could give him any in- 

 formation as to the mode of its introduction. I had little diffi- 

 culty in identifying it as the well-kown Vallisneria spiralis, a 

 common species in still water in most tropical and many tempe- 

 rate countries, and found plentifully as near to us as Australia 

 and Tasmania. During the following summer additional 

 specimens were brought to me by residents at the lake, all of 

 whom agreed in stating that it was spreading rapidly on the 

 southern shore of the lake, covering large areas in water 

 varying from 6ft. to 15ft. in depth. During a short visit to 

 the lake I saw the plant, and succeeded in obtaining flowering 

 specimens. All of these were males ; nor have any females 

 been found up to the present time. In the winter of 1895, 

 when the water of the lake stood at a high level, I heard but 

 little of it ; but towards the end of the spring, and during 

 the past summer and autumn, the case was altogether 

 difl'erent, and I was assured that it was increasing with 

 extraordinary rapidity, and that it had already crossed 

 the lake and had established fresh colonies in many 

 places along the shores. In the original locality it had 

 formed submerged masses of dense vegetation occupying 

 areas of considerable size, in one or two cases blocking up 

 the foreshore to such an extent as to compel the owners of 

 boatsheds to clear passages in order to gain access, to the 

 lake. As the level of the water fell during the summer 

 months the tips of the submerged leaves were laid bare, and 

 where they were very numerous formed a compacted floating 

 mass over which ducks and other aquatic birds walked as 

 freely as on land. Every gale washed up numerous plants 

 from shallow water, and these were frequently drifted to 

 other portions of the lake, where they became rooted in the 

 mud, thus forming fresh centres of distribution. 



