RESINOUS TRACHEIDS 



55 



At the region of contact with the tracheid wall they become 

 thicker and thereby attain a vortical distribution to an extent 

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

 position also there is a somewhat clear differentiation between 

 the plate and the wall of cellulose in point of color. Such plates 

 show absolutely 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. 6). 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 there- 

 fore subjected to a series of care- 

 ful tests to determine (i) if they 

 were structural, (2) if they were 

 resinous, and (3), if the latter, 

 to what extent. It was recalled 

 in this connection that, although 

 devoid of any special secretory 

 reservoirs in the wood, Dammara 

 is nevertheless well known for its 

 production of the resin known as 

 kauri or 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, 

 the characteristics of which are well known and described by 

 Wittstein (77, 63). Tests were applied to thin radial and tan- 

 gential sections, employing for this purpose (i) various essential 

 and fixed oils, (2) ether, (3) alcohol, (4) ammonia, (5) potassium 

 hydrate in i^ per cent solution, and (6) concentrated cupric 

 acetate. The plates were found to be very refractory with re- 

 spect to all these reagents, and in all cases no change was to 

 be observed, even after the action had extended over a period 

 of several weeks, except partially in the case of ether and 



FIG. 6. DAMMARA AUSTRALIS. Radial 

 section showing the local thickening 

 of the tracheid wall, and the occur- 

 rence of resin plates (r.p.) opposite 

 a medullary ray. x 225 



