ARID PORTIONS OF SOUTH AUSTRALIA. 137 



mulch by which the water absorbed is well retaioed are prominent 

 features in the water relations. Their relatively high temperatures 

 and the quality of good aeration are also to be considered. In the 

 vicinity of Oodnadatta, especially, where the observations were mostly 

 made, it was found that the roots of species growing on the dunes 

 had a fairly superficial type of root-system and that the roots extended- 

 far from the base of the stem. Whether, however, the same species 

 growing under other soil conditions developed another type of root- 

 system was not learned. 



The foliage of species growing on the sand dunes exhibits charac- 

 teristics of pronounced xerophytes, which may have been in part 

 attributable to the brilliancy of the light, increased by reflection 

 from the surface, and not wholly to the small water-supply. The soils 

 in other regions, for example at Copley, are in part of a very fine 

 texture, but whether the flora to be found on such soils is confined to 

 them or is modified in any determinable way by them, was not learned. 

 However, from the observations of Osbom (1914:114) more especially, 

 which were made in the Mount Lofty Ranges near Adelaide, it might 

 be expected that, in the drier portions of the state also, soils of unlike 

 texture would support dissimilar floras. The entire question regarding 

 the relation of plants to the physical nature of the soil, it may be said, 

 is so closely connected with the temperature, moisture, and aeration 

 of the soil, all of which are directly influenced by its texture, that to 

 separate the special effects of the physical nature merely from the 

 balance would be a difficult matter. 



The amount of moisture in the soil plays a very important, not to 

 say a leading, r61e among the environmental factors of the plants of 

 the dry portions of the state. Although this is well known and gener- 

 ally recognized, particular reference to certain plant reactions to 

 soil moisture may not be out of place. The limit of root penetration 

 may coincide with the depth of the penetration of the rains, or of water 

 derived from the rains, as in very dry regions. For this reason, in 

 regions where the general penetration of the rains is slight, the placing 

 of the roots of perennials is necessarily superficial. In this connection 

 it is of interest to note the belief among the wheat-growers of the 

 central portion of the state, as communicated by one of them, that 

 wheat soil when thoroughly moistened to a depth of one meter contains 

 sufficient water to mature the crop. 



In certain species, especially in Kochia sp., filamentous rootlets 

 are to be found on the main laterals which arise very soon after the 

 soil has been moistened by the rains and which cease to function when 

 the ground is dry. These occur in groups and serve the purpose of 

 quickly and very considerably increasing the absorption surface of 

 the roots. They are, in fact, "deciduous" roots and are analogous to 

 such roots as are found in many perennials of southern Arizona. 



