ARID PORTIONS OF SOUTH AUSTRALIA. 125 



rating that of each ridge. On either side of the last, and joining it with 

 the endodermisj^are water-storing tracheids, which, however; are not 

 especially well developed in the material of C. stricta studied. Within 

 the latter there extends around the periphery of the central cylinder 

 a ring of sclerenchyma which appears to be of a twofold nature, the 

 inner portion at least being fibrous, but this does hot appear 

 throughout the entire "internode," Usually within the zone of the 

 cortical conductive tissue is found that of the central cylinder, the 

 separate fibro-vascular bundles of which alternate with the ridges 

 and hence are opposite the furrows above referred to, and alternate 

 with the cortical conductive tissue. Some sclerenchyma appears with 

 the separate bundles of conductive tissue in the central cylinder. 

 A fairly thick-walled parenchyma constitutes the ground tissue of 

 the stem. 



The leading points of interest in connection with the structure of 

 the stem, from the present point of view, can be said to be very perfect 

 protection against rapid water-loss afforded by the outer cortex with 

 its heavy development of sclerenchyma, the fairly deep and narrow 

 furrows with protective trichomes, the presence of stomata in the 

 furrows only, and the close association of chlorenchjona and the water- 

 conductive and water-storing tissue of the cortex. These morpho- 

 logical features, taken in connection with the great reduction in the 

 exposed surface, point to very perfect adjustment to an environment 

 in .which a rather poor water-supply is associated with an atmosphere 

 which has a low moisture-content much of the year. 



DoDONiEA ATTENUATA AND D. LOBULATA. 



The leaves of Dodonoea attenuata have distinct dorsal and ventral 

 sides. They are of fair size and do not have so marked a xerophytic 

 appearance as most of the other species of perennials examined. This 

 characteristic is carried out in the structure as well. A cross-section 

 of the leaves shows a bifacial arrangement of the chlorenchyma. 

 That on the dorsal side is distinctly palisade and that on the ventral 

 side is well-marked spongy parenchyma. Stomata are on the ventral sur- 

 face only where they either lie on a level with the leaf -surface or in some 

 instances they were seen to project slightly above it. The epidermis 

 is not heavy. The outer walls arch outward somewhat. Sclerenchyma 

 is to be found in association with the large conductive tissue which 

 constitutes the "midrib" of the leaf, and in no other place. Short- 

 stalked, multicellular, shield-shaped trichomes are sparingly present 

 on both leaf-surfaces. The trichomes have the appearance of being 

 glandular, yet no resinous or other substance was found on the leaf- 

 surface contiguous to them in the material examined; but in young 

 leaves the surface is highly polished, as if lacquered, and it is probable 

 that the substance is a secretion derived from such trichomes. 



The structure and the more superficial appearance of the leaves of 

 Dodonoea lobulata are quite unlike those of the species just described. 



