Nos. 451-452.] ANATOMY OF THE COXIFER 



33). This feature is also prominent in a tr 

 (Fig. 32). Such local increase in thickness 

 adjacent cells in such a way that the more si 

 regions are exactly opposite, and they serve to 

 cavity gradually from above and below in such ; 

 a channel about half the usual width of the c-. 

 gradually widens upward and downward (I'ig. ■ 



.striction that we tincl a tians\erse 

 plate of variable thickness, but always of a reddish biowii tolor. 

 These plates are always thinnest in their central re- ion, and 

 they may be of uniform thickness for the grealei- part of their 

 extent. At the region of contact with the traelieid wall they 

 become thicker and thereby attain a vertical distribution to an 

 extent four or five times greater than the general thickness. At 

 such position also there is somewhat clear differentiation between 

 the plate and the wall in point of color. Such plates show abso- 

 lutely nothing of the nature of pits, and they are in no sense 

 comparable with the terminal walls of the wood-parenchyma 

 cells, except in form and position (Fig. 33). 



The peculiar position of these plates, their resinous color and 

 their simulation of both Sanio's 

 bands and terminal walls, excited 

 a suspicion as to their true nature 

 and led to the belief that they 

 might not be structural features 

 at all. They were therefore sub- 

 jected to a series of careful tests 

 to determine (i) if they were 

 structural, (2) if they were resin- 

 ous, and (3) if the latter, to 

 what extent. It was recalled in 

 this connection that, although 



devoid of any special secretory showing the local thickening of the tracheid 



reservoirs in the wood, Agathis oiit°eVmedXr7ra>l ° y^^^^^ 

 is nevertheless well known for 



its production of the resin called gum dammar. It was sus- 

 pected that the plates might be local deposits of resin, and they 

 were therefore brought into direct comparison with gum dammar. 



