608 JOURNAL, BOMBAY NATURAL MIST. SOCIETY, Vol. XXVII. 



steep lee-side of the dune, while Aerua tomentosa has obtained a footing on the 

 dune-edge itself. A detail of the edge is shown on Plate XV- A., where the two 

 pioneers are joined by Leptadenia spartium and Panicum turgidum. The former 

 of these plants may also succeed in colonising a bare dune-area, as may be seen on 

 the low dunes along the road from Jodhpur to Kailana. Generally, however, it 

 is a secondary arrival, and is rarely a dominant plant of an association, although 

 it is common. It is apparently absent from the neighbourhood of Barmer. 

 It appears that in the above locaUty the advance of the dune is actually being 

 checked by vegetation. In the elevated dune-area south of the spot, the sand is 

 already practically subdued (see Plate XV-B.), so that the amount of sand which 

 reaches the edge is insufficient to permit the dune to advance. Thus the only 

 bare or nearly bare area of the dune is a narrow, windswept belt close to the edge 

 (see Plate II), from which the sand is carried out over the plain. 



Close on the abovementioned pioneers follows the perhaps most abundant 

 plant of the region, Crotalaria burhia, which quickly overruns any sufficiently 

 estabhshed sandy area, unless the area in question is too densely covered by 

 pioneer vegetation to resist invasion effiectively. A characteristic association 

 of Crotalaria hurhia, Leptadenia spartium, Aerua pseiodo-tomentosa, and Panicum 

 ttirgidmn, covering several square miles of the elevated dune area above Loharki, 

 is shown in Plate XV-B. The grass mentioned is too weak and rambUng to be 

 able to resist the wind alone, but appears as soon as the shrubby plants have 

 developed sufficiently to afford it a support. From our observations it appears 

 that the Crotalaria is able ultimately to prevail, whenever it has obtained a- 

 footing, against the other characteristic sand plants (see Plates VII-A., XVII- 

 A & B., XX-A & B., XXXII-B., XXXIII-B.). This is perhaps the only instance 

 noticed within the region of a plant being able to crowd out others already 

 c stablished. 



The above mentioned plants generally grow in large tufts (see Plates XVI, 

 XVII, etc.), separated by bare spaces which now are invaded by other plants. 

 Conspicuous among these are several low-growing species of Convolvulus, species 

 of Polygala, etc. Breiveria latifolia, a plant of a habit not unlike that of 

 Crotalaria burhia, is often found associated with the latter, especially in the 

 Jaisalmer region, and is a typical sand plant. 



Calligonum polygonoides is another plant, chiefly growing on sand, and deserves 

 special notice, because of its remarkable ability of adaptation to diverse circum- 

 stances. When growing on dunes it prefers the very crest which it may entirely 

 monopohse. Such a case is shown in Plate XIII, which gives two pictures of 

 the first outHer of the Loharki dune area met with along our route. Parts of 

 the crest of this dune were rapidly changing as may be gathered from Plate I-A. 

 The roots of the stunted Calligonum shrubs were sometimes considerably exposed, 

 the finest ramifications, moved by the wind, tracing fine circles in the sand. At 

 the foot of this dune, the usual Crotalaria — Aerua association was observed 

 (Plate XIV-A., foreground), the Aerua extending further up the slope than the 

 Crotalaria. Nearer the crest grew a number of grasses, among which we 

 noted Panicum turgidum and Pennisetum cenchroides, a large Cyperaceoe and some 

 specimens of Indigofera argentea, together with the rare Rhynchosia arenaria 

 (sp. nov.), here observed for the first time. — On Plate XXXI-A. (left), another 

 low dune near Marwar-Lohawat is shown,, the crest of which is also clothed with 

 Calligonum shrubs. The plant was best developed round Bhikamkor. Plate 

 XXVIII-B. shows a spot near the railway station, where the vegetation consists 

 of a mixture of gravel and sand plants. Here, and especially a httle further 

 south along the railway line, where the sand layer on the gravel plain was thicker, 

 the Calligonum was abundant, growing in the form of a rounded bush, often 

 reaching 5-6 feet in diameter, having a number of branches, 1-2 inches thick from 

 the base and sometimes being in flower. For the behaviour of Calligonum as a 

 climber see under the gravel-formation. 



