206 



The medulla in the specimen is tetrarchous, a circumstance probably 

 marking the close of the individual stage of each bundle. 



In this early period of plant life the secondary tracheids of the xylem have 

 fully developed bordered pits in their radial walls, the lamellae with their tori 

 being distinctly seen under a medium power objective. 



In the phloem the structure is precisely a forerunner of what is found in 

 the bark of mature trees, for under a 70- and, more especially a 325-magnihcation 

 it is found that the uniseriate concentric rings of hard bast cells alternate with 

 three rings made up of a uniseriate parenchyma, separating sieve tubes of a 

 uniseriate ring. The similar staining and general resemblance of the former 

 appear to indicate a xylemic origin, or at least a close affinity to that stnicture. 



The oleo-resin cells of the bark are just beginning to evolve even at this 

 early period of that formation, and are easily seen in the phloem substance. 



\\'hen dealing with the mature wood, a number of transverse sections were 

 cut, the prominent feature upon examination being the irregular manner in which 

 the cells, containing the manganese compound, are scattered throughout the 

 tracheids. Sometimes they occur closely packed on either side of the autumnal 

 wood, whilst in other instances they are sparsely scattered throughout the vernal 

 growth, or again, in an area of three consecutive years of autumnal and spring 

 growth, thev are not found. These features are well shown in the Figures 136 

 to 139. 



The whole of the secondary wood in these sections consists of prosenchy- 

 matous cells of strongly thickened walls, almost uniformly hexagonal on the outer 

 walls and circular on the inner. Those of the autumnal series are thicker than 

 the others, all being arranged in radial rows with cells of \-arying diameters. 



A radial section shows that the parenchymatous cells of the medullary 

 rays are fewer in number than those of C. glauca, averaging say from fi\-e to 

 twelve cells high, and are narrower than obtains in that species, and also that the 

 outer cells, as in that species, are of similar structure to the inner, and not 

 tracheidal in nature. 



In a tangential section (Figure 137 it will be noted that the parencliymatous 

 cells of the medullary rays are apparently rather freer of cell contents than obtains 

 in most species of Callitris, which fact may be thought to be a slight specific 

 difference, but this is not reliable enough for systematic classification, for sections 

 taken in other parts, such as in Figure 138, show quite the reverse of this feature, 

 for all the ray cells appear to be filled with tlir Ijiown-coloured substance, — 

 manganese compound. 



These parenchymatous rays are from one to twelve cells high, and linear or 

 fusiform in shape in the tangential view. (Figure 137.) 



