54 



ANATOMY OF THE GYMNOSPERMS 



The dark plates closely resemble Sanio's bands, for which they 



might very readily be mistaken upon casual observation, or they 



might likewise be mistaken for terminal 

 and unpitted walls. In Dammara australis 

 these features are presented in their typ- 

 ical form. The transverse section shows 

 such elements to be numerous and dis- 

 posed in radial rows on each side of the 

 medullary ray (fig. 5). In a radial section 

 they present the 

 same fibrous and 

 fusiform charac- 

 ter as in Arau- 

 caria, but, in 

 addition, the wall 

 usually experi- 

 ences a marked 

 increase in sec- 

 ondary growth 

 within the region 



exactly opposite a ray (fig. 6). This fea- 

 ture is also prominent in the transverse 



section (fig. 5). Such local increase in 



thickness always arises in adjacent cells 



in such a way that the more strongly 



thickened regions are exactly opposite, 



and they serve to constrict the cell cavity 



gradually from above and below, in such 



manner as to leave a channel about half FlG -5- DAMMARA AUSTRA- 



LIS. Transverse section 



the usual width of the cell cavity, which showing the disposition of 



gradually widens upward and downward 



(fig. 6). It is at the position of maximum 



constriction that we find a transverse 



plate of variable thickness, but always of a reddish-brown color. 



These plates are always thinnest in their central region, and they 



may be of uniform thickness for the greater part of their extent. 



FIG. 4. DAMMARA AUSTRA- 

 LIS. Tangential section 

 showing the relation of the 

 resin plates and the medul- 

 lary ray, and a fractured 

 plate (r.p.). X 225 



the resinous tracheids on 

 opposite sides of the med- 

 ullary ray at r.t. X 300 



