THE VEGETATION OF THE COAST. 



69 



dunes ' : (fig. 28) insidiously advancing inland, do great damage- 

 burying fertile fields, filling up valuable flax-swamps, choking water- 

 courses, and overwhelming forests, plantations, pasture-lands, and 

 even human dwellings. Happily nature has done much to stop such 

 inroads, and the wandering dunes of New Zealand are chieflv tin- 



>' .-.'.,._ ./ 



result of damage dpne by grazing animals and by burning. 



In order that a plant can live on drifting sand it must have the 

 power of binding that unstable compound into a firm mass. Plants 



FIG. 28. General view of a Wandering Dune occupying ground formerly good 

 grazing-land. Dime-area of western Wellington. 



Lands Department.] 



[Photo. L. Cockayne. 



with rapidly growing underground stems, which have the power of 

 rooting near the tips of the branches and putting forth new shoots as 

 fast as the old ones are buried, are sand-binding plants par excellence. 

 With few exceptions, wherever sandhills exist on the globe, such 

 plants accompany them. 



In New Zealand there is a most excellent example in the pingao 

 (Scirpus frondosus) (fig. 29). Its thick, rope -like stems, commonly 

 called roots, form a perfect entanglement inside the dune, and its 



