94 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



He particularly mentions Phormium tenax (the New Zealand flax), 

 Cy perns ustulatus, Pteris esculenta, &c, as displaced by European grasses 

 and clovers, as these sap away the nourishment and so starve them. 

 Even shrubs five to eight feet high, as Leptospermum, are destroyed by 

 grasses. This is also replaced by Epacris purpurascens from New South 

 Wales, and by Eucalyptus globulus seedlings and wattles (Acacia) which 

 out-top the shrub. Bobinia pseud-acacia spreads and stops native growth 

 by its numerous root-suckers. Leptospermum and Pomaderris are also 

 killed by furze and broom, while Bosa rubiginosa (sweetbrier), B. canina 

 (dcg-rcse), and Bubus fruticosus (blackberry) exclude light and air by 

 their curved branches. 



The rivers, too, have become impeded by Salix babylonica, S. fragilis, 

 &c, while Nasturtium amphibium often grows many feet in length, with 

 a stem nearly an inch in diameter, and even rises 3 to 5 feet out of water, 

 thus, with Anacharis (Elodea), choking the rivers. The waste lands by 

 new roads in New Zealand are also infested by English weeds, as docks, 

 thistles, Juncus bufonius, &c. 



As an experimental result of the struggle for existence with an 

 inhospitable soil, an experience of Messrs. Livington and Jensen is 

 instructive.* They grew a number of wild plants in tubs full of sand, 

 in three degrees of fineness ; the particles of the finest grade had an 

 average diameter of 0-02 mm. ; those of the medium grade 0*6 mm. ; 

 and those of the coarse 1*15 mm. 



The result is shown in three photographic representations. 

 In the first the tub has a collection of vigorously growing plants. 

 In the second they are much inferior in size, while the plants are reduced 

 in number. In the third such is still more the case.t 



The heights of some of the plants were in centimetres as follows : — 

 Potcntilla anscrina in finest, medium, and coarse sand, respectively, 

 20-23, 8-10, 6-8; Verbena hastata, 14-19, 5 8, 2-3; Poa pratensis, 

 15-20, dead, dead ; Poa comprcssa, 28-40, nearly dead, dead. 



Oxalis cernua furnishes an instance of extraordinary diffusion. It 

 has an umbel of drooping golden-yellow flowers. It is a weed about 

 Cape Town, and fruits there. In 1804, a few of the tiny bulbs by which 

 it is also propagated were sent to Father Hyacintho, the Professor of 

 Botany, Valetta, Malta. During the hundred years which have elapsed 

 since that date, it has spread all over that island as well as Gozo. By 

 the exportation of oranges, &c, it reached Egypt about 1820, Gibraltar 

 in 1829, and various other places along the coasts of the Mediterranean 

 Sea, so that it is now to be found at different places from Egypt to 

 Morocco and from Gibraltar to the Greek Islands, as well as in the 

 Canary Islands. In Malta it is most prolific ; fields often look as yellow 

 as an English meadow with buttercups. It finds a home everywhere, 

 even on the tops of high walls of the fortifications, and it clothes the 

 roadsides instead of grass, having expelled the native verdure. For a 

 century it has thus proved itself to be perfectly adapted to thrive in 



* " An Experiment on the Relation of Soil Physics to Plant-growth," Bot. Gaz 

 vol. xxxviii., p. 67. 



f All the plants in the three tubs were supplied with salts essential for growth, viz. 

 KH PO,, Ca(NQ 3 ),, MgSO„ NaNO s , CaCl,. 



