SYSTEMATIC rOSITIOX OF jriTHASTEMOX. '205 



elongated wodge witli a, long tlnead <at tlie apex. The thmul which lies 

 deep within tlie xylera, after having finished its iDhysiological function, is 

 found dead and bmied deep in the xylem. The vertical threads are com- 

 posed only of rounded parenchymatous cells wliich are rounded at the basal 

 portions but by and by become elongate towards the apex, es|»cially iu the 

 apical portions which are composed of a single row of ceEs. 



The horizontal threads become more and more slender as they recede 

 from the ilower-regiou, and show no more differentiation of i>eripheral paren- 

 chymatous and central tracheidal tissue, and in much remoter regions, say 20 

 or 30 cm. frora the flower-regions and in the part of the root where it attains 

 nearly 2 mm. in diameter (in main or adrentive roots), tliey remain as 

 threads composed each of a single row of celLs in or just above the cambium- 

 layer. This shows how widely they are spread over the host root. They 

 are by no means straigbt, but always anastomosing and rimning in a zig- 

 zag manner. In longitndinal sections of the host-i-oot, they appear, not as 

 straight hnes, bnt as interrupted or dotted lines. The vertical threads are 

 usually larger in parts near the floT'al polster, bnt become shoi-ter in remoter 

 regions. As the horizontal threads reticulate themselves, so do the veiiical 

 threads in the region of the xylem, mostly at their apical poiiions towards 

 the center of the pith. There the vei-tical thi-eads push ont forraless branches 

 towards the apex of the host-root, along its long axis, parallel to the 

 horizontal threads in the bast. Here we liave another kind of horizontal 

 threads which connect the vertical threads in the xylem, making an iiTegular 

 network. This network is com]TOSPd of iiTegnlar threads comixjsed of single 

 rows of roundod cells which are very much larger than tliose in other parts 

 of the intramatrical tissuc, and are of xevv irregular amoeboid shaf)e. The 

 vertical threads ■«hich vun usnally side by side with the medullary rays are 

 easily distinguished from theii' companions by their having elongated rounded 

 cells fnll of plasmas, with much larger unclei, and sraooth and ranch tlunner 

 ■walls. The cells of the medullary rays, in contiust to those of the vertical 

 threads, are usually rectangular, and have xMtted and tlucker walls. The 

 intramatrical tissne is generally distinguished from the host tissue by its 

 taking a rauch deeper stain with any staining matter, for example with 



