ACACIAS OF SOUTH-EAST QUEENSLAND. 45 



V. — Acacia maideni F.v.M. differs radically in its histology 

 from all other species examined. The vessels of the xylem 

 are few and small, and in young stems all are elongated in a 

 radial direction. The medullary rays are narrow and drawn 

 out radially, and the cells of the wood parenchyma are less 

 thick- walled than usual. Much of the water and dissolved 

 minerals of the ascending sap must pass by osmosis through 

 the wood-cells of the alburnum. 



Passing through the phloem the medullary rays take a very 

 wavy course. In tangential section they measure 110-285 fx 

 by 8 to 12 fji. The pith is of the usual structure and contains 

 a few idioblasts. Strands of sclerenchyma are found in the 

 cortex, but this tissue is not as strongly developed as in any 

 of other acacias examined. Surrounding the vessels of the 

 xylem the wood- cells are larger and their rows more irregularly 

 constituted (tangential section) than elsewhere. In the cells 

 of the cortex numerous tabulate crystals were noted. (Plate V.) 



VI. — Acacia implexa Benth. The young stem of implexa 

 1-2 years old shows the layer of epidermal cells with their 

 external thickening of cutin. The pith and xylem are of the 

 ordinary type, but the phloem is mainly of soft bast, and 

 the sclerenchyma is only moderately developed. In all other 

 respects it agrees with the characteristics already laid down. 



