Cheeseman. — On Vallisueria spiralis in New Zealand. 387 



Although I had no doubt that Vallisueria had been pur- 

 posely introduced, it was some time before evidence of the 

 fact was obtained. I was at length informed by Mr. E. 

 Bartley that in 1885 he received some living plants from Dr. 

 Ealph, of Melbourne. These he cultivated for some time in a 

 small aquarium in his garden, but eventually planted one of 

 them, a male, in a secluded nook on the south side of the 

 lake. A year or two afterwards he revisited the locality, 

 and failing to find the specimen, concluded that it had died. 

 It is from this single plant, however, that the lake has been 

 stocked. As only one sex was planted, propagation by seed 

 has been out of the question, and the whole of the plants now 

 growing in the lake have been derived from offsets accidentally 

 detached and drifted to fresh stations. 



Vallisueria has increased so rapidly during the last two 

 years, and has shown such aggressiveness and facility of dis- 

 tribution, that it will probably increase still further. Its 

 spread in the past has naturally alarmed people not fully 

 acquainted with the conditions of its growth, and surmises 

 have been made to the effect that it will gradually spread into 

 deeper water until a considerable portion of the lake is 

 occupied with it. The water-supply of the Borough of 

 Devonport is drawn from Lake Takapuna, and the Mayor 

 and Councillors of the borough have several times had under 

 their consideration the probable effects of the spread of Vallis- 

 neria upon the purity of the water. I am of opinion, however, 

 that there is little cause for alarm. From what I can learn 

 of the growth of Vallisneria in other countries, it appears 

 that it usually lives in water from 6ft. to 12ft. or 15ft. in 

 depth, rarely or never flourishing in deeper water. It is pre- 

 cisely in waters of these depths that it has become established 

 in Lake Takapuna, and beyond those limits it probably will 

 not advance. Fortunately, Takapuna is a deep lake, a great 

 portion of it varying from 12 to 25 fathoms in depth. In 

 many places the shallow water fringing the shore is a mere 

 strip, and with the exception of a bay at the northern end it 

 is nowhere very wide. Consequently there is no risk of 

 Vallisueria doing more harm than will result from the for- 

 mation of a narrow fringe around the shores of the lake, 

 interfering to some extent with bathing and boating. 



The question at once suggests itself whether Vallisneria, 

 having effected a lodgment in this country, will spread into 

 other localities. The shallow lakes and sluggish streams of 

 the middle Waikato basin are places where it might cause 

 serious trouble by choking channels of drainage or even navi- 

 gable streams. We have before us the instance of the Ameri- 

 can Elodea {AuacJiaris) canadensis, a plant closely allied to 

 Vallisneria, which made its appearance in Britain about the 



