379 



The tangential section is microscopically no less a beautiful object than 

 the radial, and Figures 263-4 show clearly the main features of distinction between 

 it and cognate genera, the most important being the occurrence in well-defined 

 elongated groups of pitted cells on the tangential walls, a rare occurrence in 

 Australian Conifers. 



The " string of bead-like" structures, Figures 263-4, so clearly shown on 

 the tracheid walls, are the pitted cells cut vertically, or seen in profile. 



The transverse sections in Figures 261-2 show Lhe less regular polygonal 

 shape of the tracheids of the xylem of this genus, and also the scarcely 

 distinguishable autumnal growth in the former, probably due to the equable 

 seasons of its habitat. 



V. BARK. 



{a) Economic (vide Chemistry). 



(b) Anatomy. 



This bark in some respects resembles that of the Arancanas. It has not 

 the well defined lines of structure to be found in Callitris, for tiie sclerenchymatous 

 fibres resemble those of the Arcuicarias rather than the Callitris, and in cross- 

 section, given in Figure 267, they can be seen scattered amongst parenchy- 

 matous cells and sinuous medullary rays. The large empty cell in the centre 

 of the picture is an oleo-resin cavity. Throughout the bark substance are masses 

 of sclerenchymatous fibres. 



(c) CHEMISTRY OF THE OLEO-RESIN. 



Theoretical. 



This sample of freshly collected oleo-resin was sent to us by the Depart- 

 ment of Agriculture, Queensland, and was obtained from trees growing in their 

 natural habitat. When received it was of a thin, pasty consistency, contained 

 a large amount of essential oil, and had a somewhat aromatic odour and a 

 bitter taste. The material was freshly exuded, so that its constituents could 

 hardly have undergone much change ; the action of the air, and other con- 

 tributing influences towards alteration, had been retarded, as the resin was sent 

 in closed vessels. The oleo-resin was thus largely in its natural condition. 



The general method of investigation was similar to that carried out with 

 the latex of Araucaria Cunninghamii , and it was found to contain many similar 

 substances to those isolated from that material ; so that, broadly speaking, the 

 general constituents are common to both trees. The oleo-resin of Agathis vobitsta 

 contained a gum similar in composition with that isolated from the latex of 

 Araucaria Cunninghamii , although it is present in less amount than in the exudation 



