269 



Fig. 10. 

 Diagram of a transverse section of 

 the assimilating shoot of Casuarina 

 distyla. All lignified tissue is shown 

 black. The dotted line represents 

 the limit of the chlorenchyma. 

 Camera lucida outlines, X 16. 



Fig. 11. 

 Diagram of a transverse section of the 

 assimilating shoot of Casuarina stricta. 

 All lignified tissue is shown black. ■ The 

 dotted line represents the limit of the 

 chlorenchyma. Camera lucida outlines, 

 xl6. 



The shoot of C. lepidophloia is bounded by a moderately thick cuticle which 

 extends about half-way down each furrow. The lower portions of the furrow 

 are not thickly cutinised, and in this portion the stomates are arranged in 

 usually four straight rows which extend down the whole length of the shoot. 

 At the base of the furrow arise a few branched hairs. They are not numerous. 

 The chlorenchymatous tissue is much reduced and occupies only a small space 

 each side of the furrows. Between each chlorenchymatous group a mass of 

 sclerenchymatous tissue is developed. The cortical region contains no 

 parenchymatous cells save those of the medullary rays. In C. distyla and C. 

 stricta there is a considerable parenchymatous cortex. The bulk of the cortex in 

 C. lepidophloia is occupied by bast fibres. Running through the cortex from 

 node to node are leaf traces, one opposite each rib of the shoot. The traces 

 consist of collateral bundles of xylem and small phloem elements. Surroimding 

 each bundle and extending to the base of each furrow lies a water transfusion 

 tissue. These cells are approximately isodiametric, have cellulose walls, and 

 are pitted on all their walls. 



The conducting tissue occupies the central portion of the shoot. The xylem 

 consists of spirally thickened and annular vessels. Secondary thickening had 

 commenced in all shoots examined and the xylem formed a continuous band 

 around the medulla. The phloem consists of small-celled elements with densely 

 granular contents. The medulla consists of a tissue which does not appear to 

 be described elsewhere in the Casuarineae. It consists of very thick-walled cells 

 connected by numerous pits. The walls are lignified, and when seen in transverse 

 section present somewhat the appearance of large fibres. In longitudinal sec- 

 tion, however, it is seen that they are tracheidal in form and perform probably 

 the function of water storage. In addition such a central tissue has a great 

 mechanical advantage to a plant such as C. lepidophloia in which the switch-like 

 shoots are continually exposed to a vigorous wind action. Interspersed with 

 these tracheidal cells are a few cells containing tannin. In C. distyla the pith 

 is slightly sclerised. 



From this central tissue, medullary rays run through the conducting system, 

 through the cortex, and terminate at the bases of the furrows. It is somewhat 

 remarkable that every cell in the rays is full of tannin which stains a violet-black 



