29 



the leaf bundle and the palisade layer and in the centre of the spongy mesophyll 

 tissue, but surrounded by parenchymatous endodermal cells. Longitudinal 

 sections invariably showed them to be cavities rather than glands, certainly not 

 canals or ducts as obtains in non-Australian genera of the Order. They appear 

 to be of lysigenous origin. 



Below each gland is a small bundle with a normal orientation, the phloem 

 having thin-walled cells irregularly arranged, the xylem having thicker-walled 

 cells, disposed in a more regular, radial series than those of the phloem, the whole 

 being accompanied more or less by transfusion tissue. 



For anatomical descriptive purposes it was found to be much more satis- 

 factory to take a section through the extremity of a branchlet just below the 

 internode, and through the three concrescences, rather than through an individual 

 concrescence, for such a section is found to be most symmetrical, and in outline 

 forms geometrically an almost perfect trefoil. 



This geometrical outline in a measure corresponds in a general way to that 

 of some forms of Pinus leaves which have two bundles, whilst in this instance the 

 stele, being the branchlet, contains three or more, and having central radiating 

 cells dividing it into the wedge-shaped bundles of the branchlet or central column. 



Such sections have been taken when describing and figuring the leaf 

 anatomy of each species, as they give a better idea of the correlation of each 

 leaf to the stem structure, and also their correlation in performance of functional 

 work to each other. 



Viewed then as a whole, the leaf sections present some interesting features, 

 as for instance, the variation in the disposition of the parenchymatous transfusion 

 tracheids, the stone, as well as the endodermal cells, which are well shown 

 in the illustrations, and when there is no oil cavity these latter occur in a group 

 in each foil ; but as an oil reservoir gradually comes into the vision, it is seen to 

 separate them, and they then form an encircling ring around it, as well as the 

 stele, and so with each oil cavity of the corresponding leaf. The parenchymatous 

 cells containing the manganese compound are more numerous below the junction 

 of the foils where the epidermal and chlorophyll parenchymatous cells are absent. 

 This latter arrangement has already been fully discussed. 



The anatomical characters of the leaf of Callitris, such as the arrange- 

 ment of (i) assimilatory and transpiratory surfaces, (2) the palisade cells, 

 (3) cells of the fundamental tissues, and (4) sclerenchymatous cells, render 

 some aid in systematic work ; whilst the position of the oil cavities may practi- 

 cally be said to be common to all the species, for whatever little variation there 

 is in connection with these, it is of too minor a nature upon which to found 

 specific differences. 



