276 JOURNAL, BOMBAY NATURAL HIST. SOCIETY, Vol. XXVIL 

 2. Climate and Vegetation. 



From what has been said above, it is clear that the chmate is hostile to all 

 vegetation, only plants possessing special adaptations being able to establish 

 themselves. These adaptations are in general of two types, having two distinct 

 objects in view : to enable the plant to obtain water, and to retain it when 

 obtained. Those interested in the anatomical pecuharities of the plants of the 

 region are referred to the paper by T. S. Sabnis : " The Physiological 

 Anatomy of the Plants of the Indian Desert," at present appearing in the 

 Journal of Indian Botany. 



The struggle for existence between the plants, of the same or of different spe- 

 cies, is practically non-existent, there being plenty of vacant spaces, and the 

 formations being generally of the open type. The chief exceptions to this rule 

 are the following parasites -.—Cuscuta Tiyalina (growing on many . host-plants, 

 see Vol. XXVI, p. 543), Striga ocobancheoides (on Lepidagathis trinervis), Striga 

 eupJirasioides (on grasses, etc.), Cistanche tuhulosa (on Capparis decidua, see plate 

 XXII-B.) — The case of Crotalaria hurhia is discussed under the sand formation. 

 Possibly the abundance of this plant may have something to do with nitro- 

 bacteria, Uving in symbiosis with the plant in its root nodules. 



Many seeds fail to germinate, and numbers of seedlings are destroyed, thus 

 never reaching maturity. 



The bulk of the vegetation consists of a kind of scrub made up of shrubs and • 

 perennial herbs, capable of great drought resistance and of a period of compa- 

 rative rest, extending throughout the greater part of the year. There are few 

 trees to be seen, and these are stunted and generally thorny or prickly, thus 

 protecting themselves against plant-feeding animals. Of the latter, there are 

 vast herds of camels, cattle, sheep and goats, forming the chief wealth of the 

 rural population, and appearing to thrive in spite of the arid nature of the 

 country (Plate XXXII-B.). The presence of these herds is a factor of some 

 importance in the economy of the region, certain plants being kept down, while 

 others remain untouched. Thus it is sometimes impossible to find a fairly com- 

 plete specimen of many plants over large areas, the branches being eaten, and 

 only the woody base left. Plate XXXIV-A. shows a case, where a specimen of 

 Heliotropium undulatum (the plant to the left) has escaped total destruction 

 owing to its being accidentally protected by an ant-hill. On the other hand, , 

 the specimen of Sericostoma pauciflora to the right is not touched although 

 unprotected, in spite of its being a close relative of the former plant. Some- 

 times a spiny shrub protects a plant, otherwise greedily eaten by animals. A 

 case of this is shown in Plate XXXIV-B., where a line specimen of the grass 

 Andropogon annulatus, reaching the unusual height of eight feet, has taken refuge 

 among the branches of the very prickly Zizyphus rotimdifolia. The luxurious 

 growth of the grass is due to the local presence of moisture in the gravelly soil. 

 Of unprotected specimens in the same habitat, practically only the roots were 

 left. Below we give a hst of the plants especially liked by camels : Capparis 

 decidua, Salvadora oleoides, Haloxylon salicornicum, Fagonia cretica, Crotalaria- 

 hurhia, Clerodendron pMomidis, Calligonum polygonoides, Indigofera ovalifolia. 



The proper desert plants may be divided into two main groups : those depend- 

 ing directly upon rain, and those depending on the presence of subterranean 

 water. 



The first group consists again of two types : the "ephemerals" and the " rain 

 perennials," — The ephemerals are delicate annuals, apparently free from any 

 xerophilous adaptations, having slender stems and root-systems and often large 

 flowers. They appear almost immediately after rain, develop flowers and fruits 

 in an incredibly short time, and die as soon as the surface layer of the soil dries 

 up. We did not come across any plants of this type, which may however have 

 been due to the fact that our visit took place towards the end of the rainy season. 



