512 JOURNAL, BOMBAY NATURAL HIST. SOCIETY, Vol. XXVII. 



between the sand and gravel, from an ecological point of view, is then, that 

 the capillary cavities between the grains of the former are capable of retain- 

 ing water, but that the surface layer, as it dries up, is liable to be shifted hy 

 the wind ; while the surface layer of the latter remains firm, in spite of which 

 it is unsuitable to support vegetation on account of deficiency in water. 



From what has been said it is not surprising, that the colonisation of a gravel 

 area is a slow process, and that bare patches, such as are shown on Plate XIV- 

 A., are of frequent occurrence. In this particular case it is possible that another 

 factor has been active, the locality being crossed by several foot-paths, and by 

 the " high-road " from Bap to Jaisalmer visible at the farther edge of the bare 

 area. Plate XIV-B. shows a detail of the habitat mentioned. The surrounding 

 association consists of high, tufted grasses and Leptadenia spartium, whUe on 

 the bare patch itself grow isolated specimens of Eleusine aristata and E.aegyptiaca , 

 Aristida mutabilis, Fagonia cretica, Cleome papillosa, Boerhaavia diffusa. All are 

 common gravel plants, and at least the two last, typical of the formation. Boerlm- 

 avia is perhaps best adapted, having a strong woody tap-root penetrating to 

 a considerable depth. Its branches are weak and very long, and wither at the 

 end of the rains. Instead of spreading out in all directions, which they of 

 course would do, were there no wind, the branches are kept parallel by the 

 action of the wind, those to windward being thrown right over. 



Other typical gravel plants have stiff, more or less woody branches, which 

 lie flat on the ground. An example of this habit is furnished by Gorchorus 

 antichorus (Plate IV-B.), the branches of which form dense mats, and should 

 be able to resist the long period of drought, producing new leaves during 

 the rainy season. This plant has a tajD-root of enormous length. Seetzenia 

 orientalis (Plate IV -A.), on the other hand, has weak, almost succulent, short 

 branches radiating from a very short central stem, forming a star-like plate on 

 top of the tap-root. 



Of other typical gravel plants of the flat-growing habit we note first 

 Tribulus terrestris and T. alatus, the former being universally distributed 

 throughout the region, the latter rare, and only observed by us in the neigh- 

 bourhood of Jaisalmer. Further, the following ' species of Indigofera : I. lini- 

 folia, abundant in the east along the railway fine, absent in the north along 

 our route, /. trigonelloides, fairly common in the eastern and northern part 

 our region, absent in the west, I. enneaphylla, a rare plant, only found at 

 Mandor and Balarwa, I. anabaptista, common all over the region, formerly 

 supposed to be confined in India to Sind and the Punjab, and to be 'very 

 rare. At Balarwa all these species of Indigofera were associating with 

 Gorchorus antichorus, the plants giving the ground a peculiar, spotted appear- 

 ance (Plate XXVIII-A., foreground). 



There is also a group of gravel plants with a bushy habit. Here belong the 

 already mentioned Leptadenia spartium (also on sand), Fagonia cretica (also on 

 rocks), Gleome papillosa ; further Breweria latifolia (also on sand and rocks), 

 Scricostoma paucifiora, and most species of Heliotr opium (Plate XXXIV-A.). 

 Salvia cegyptiaca, a shrubby Labiate is typical of the formation, but is absent 

 from the western half of our region. Blepharis sindica prefers gravel to other 

 habitats, and is abundant everywhere. The same may be said of Anticharis 

 linearis, whUe A. glandulosa var. coerulea is rather rare, and only found south of 

 Jaisalmer. 



The parasite Striga euphrasioides mostly attacks grasses on gravelly soil. The 

 plant was not found between Phalodi and Jaisalmer. 



Mollugo nvdicaulis and M. cerviana are two small annuals growing on fine 

 gravel. They both have rosulate leaves. 



A plant with an interesting distribution along our route is Haloxylon salicor- 

 nicum, which we only found in the neighbourhood of Sodakoer. It suddenly 

 appeared a few mUes east of this village, often growing on a small mound (Plate 



