226 



The most important features of difference in the leaf structure, from those 

 of its congeners, are >^i^ the presence of many sclerenchymatous cells in the spongy 

 parenchyma of the mesophyll ; (2) the absence almost of a well-defined mass of 

 transfusion tissue, as obtains in C. calcarata and C. robusta, and ^3) the absence 

 of the manganese compound in the parenchymatous endodermal cells. 



The dorsal surface may be said to be concavo-convex, and it is in the concave 

 portion the stomata occur, such as is also found occasionall\- in C. calcarata. 



The epidermal cells are larger proportionateh- than those of its congeners. 



Figure 142 illustrates a section taken just below the free ends of the leaves, 

 and shows, as in other species, how the three decurrent leaves form, along \\ith 

 the central axis of the branchlet, one whole. The palisade cells are poorly developed 

 in these leaves and e^•en the spongy tissue of the mesophyll is less than that of 

 other species, their place being taken by an unusual proportion of parenchymatous 

 endodermal tissue, the cells of which can be seen to be empt}' and closely packed 

 around the central axis and oil cavities, filling the base of the leaves and also 

 enclosing the leaf bundles. The transfusion tissue is only fairly well developed 

 as compared with other species of Callitris. One marked characteristic feature 

 of C. rhomboidea leaves, is the unusual number of sclerenchymatous cells in the 

 spongy tissue of the leaves, although not so well seen in this Figure as in 

 Figures 144-6 where the}' can be traced as dark irregular bodies in the mesophyll. 



Figure 143 gives the contour in section of the three leaves when the branch- 

 let is fully formed, and they are beginning to be thrust apart. It \\i\\ be observed 

 in this illustration that the phloem of the branchlet forms a complete circle 

 enclosing the xylem together with its median pith cells; the decurrent channel 

 has gradually widened, and the dorsal surface is convex in the centre and 

 concave at the sides, where are situated the stomata, a feature which marks this 

 as a coastal species, and in which respect, therefore, it differs from the Callitris 

 of the interior. Figure 144 is reproduced as it shows the effects in the contour 

 of a leaf when a branch trace begins, as in the base of the upper leaf. The 

 depressions on the dorsal surfaces locate the stomata. Note the sclerench\-matous 

 cells in the lower leaves. Figures 145-6 are different sections taken in the 

 neighbourhood of the oil cavities in the upper portion of the leaves. 



(c) Chemistry of the Leaf Oil. 



This material was collected at the Spit, near Sydney, New South Wales, 

 on the 25th January, 1907. 



The terminal branchlets alone were used, and although a few fruits were 

 present, they contained no oil. The distillation was continued for six hours, but 

 the yield was very small — 616 lb. only giving 2,\ (J^- of oil, equal to -0335 per cent. 



