ch. in FIXATION OF UNSTABLE SOILS 285 



not only branch and branch again, but give out fresh 

 roots at the nodes and thus hold the soil. The best 

 known of these are the Ipomaea biloba, a Convol- 

 vulaceous plant, and the Spinifex squarrosus, a creeping 

 grass with globose heads. To these may be added 

 Cyperus arenarius, Canavalia obtusifolia, Hydro- 

 phylax maritima, Spermacoce hispida, Launaea 

 pimiatifida, Pupalia orbiculata, and Payidanus 

 odoratissimus. 1 



In Ceylon the same plants are to be found, with 

 various shrubs, such as Scaevola Koenigii, S. Lobelia, 

 Clerodendron inerme, Azima tetracantha, and the 

 Palmyra Palm (Borassus jiabellifer). These, in most 

 places, spring up in sufficient abundance to check the 

 march of the dunes before they have got beyond a 

 second range of hillocks. On the sandy shores of the 

 Red Sea numerous plants belonging to the natural 

 orders Chenopodiaceae and Zygophyllaceae keep the 

 soil together, as well as Statice axillaris, Bergia 

 sujfruticosa, Cyperus cruentus, and creeping grass, 

 Aelurops repens. 



It may be necessary to take more elaborate measures 

 to fix the invading sands, and the method adopted in 

 the French dunes will now be described. 



The first step taken is in erecting, at the foot of 

 the outer line of sand-hills, or rather between it and 

 the sea, close on the beach above high-water mark, a 

 long row of boards, not unlike thin railway sleepers in 

 size and appearance. These boards are stuck firmly 

 into the ground, so that they may not be overturned 

 by the pressure of sand and wind. They are not set 

 in touching each other, but a short distance apart, the 

 space between them being about 2|- cm. (1 in.). This 

 not only reduces the pressure from wind and sand, but 

 it allows a certain quantity of the latter to trickle 

 through the apertures, as it gets accumulated on the 

 windward side, and thus to enlarge the base of the new 



1 "Sand-binding Plants," by V. Subramania Iyer, in Indian Forester, vol. 

 xxxv. No. 2. 



