124 PLANT HABITS AND HABITATS IN THE 



NOTES ON CERTAIN OTHER SPECIES OF THE REGION. 



BoSSIiEA WALKERI. 



This is a low shrub of rather loose habit of growth and leafless. 

 The branches are flattened, almost winged. The species was observed 

 in the neighborhood of Ooldea, where it occurs mainly on dry, sandy 

 ridges.* A cross-section of a stem shows the peripherally placed 

 chlorenchyma, which is fairly distinctly grouped and made up of a short 

 form of pahsade cells, three layers or so in thickness, and, within the 

 chlorenchyma, the central portion of the stem of which is largely 

 composed of parenchyma, much of which was seen to contain starch- 

 like granules. A leading feature of all the parenchymatous tissue is 

 the relatively heavy walls, which are pitted. Sclerenchyma occurs 

 in connection with the conductive tissue and is most abundant at the 

 central portion of the stem, although large and conspicuous masses 

 are to be found not far beneath the stem margins. The epidermis is 

 made up of relatively deep cells, with a heavy cuticle, and is underlaid 

 by a subepidermal tissue, very regular in appearance, and composed 

 of rectangular cells placed at right angles to the stem surface and which 

 may or may not contain chlorophyll. A cross-section of the stem shows 

 that the surface is not plane but ridged. The stomata appear to be 

 confined to the bottom of the furrows between the latter. They are 

 situated somewhat below the general surface of the stem, therefore, 

 and the guard cells are protected by a fairly heavy cuticular develop- 

 ment. No trichomes of any kind were found on the material studied. 

 Casuarina stricta. 



The equisetum-like branches of Casuarina stricta^ which carry on 

 the leaf function, have an intricate structure which appears to cor- 

 respond in the essential points to that of C. equisetifoUa as described 

 by Solereder (1899 : 885) . Only certain features, clearly associated with 

 the xerophytic habit of the species, need for that reason be referred to 

 in this place. The structural arrangement is intimately associated 

 with the presence of longitudinal grooves and ridges characteristic 

 of the "internodes" (fig. 17). The chlorenchyma, pahsade tissue, is 

 confined to the sides of the grooves, and in cross-section of the stem 

 it appears as separate masses. Between the chlorenchma, and between 

 it and the periphery of the stem, there is only or mainly sclerenchyma. 

 Stomata are confined to the sides and bottoms of the grooves. Tri- 

 chomes are present in the grooves, from the bottom of which they take 

 their origin. The inner portion of the chlorenchyma is only sUghtly 

 more deeply placed than the bottom of the grooves. A distinct cell- 

 layer, endodermis, bounds the inner face of the chlorenchyma. 



Cortical conductive tissue Ues opposite the ridges and hence some- 

 what deeper than the chlorophyll-bearing tissue, but on a line sepa- 



*Spe page 88 and plate 29a. 



