28 ART. 10. — S. KÜSANO : STUDIES ON THE PARASITISM 



colour and density as in the stem of many trees (Fig. 21). 

 As is well known, the duramen of the stem is characterized, 

 not by any modification in the original structure and thickness 

 of the cell-wall, but merely by changes of the material pro- 

 perties of the wall, as well as of the contents. The original 

 physiological work (the purely mechanical function is not here 

 considered) of the cells is rendered impossible by the accumu- 

 lation of deposits of some infiltrating bodies or by the formation 

 of thyloses within the vessels and cell-lumina. The change into 

 duramen in the haustorium is in most respects similar to that 

 in the stem, but here it is accompanied by a process of dis- 

 organization. 



The cell-walls of the pith as well as of the medullary rays 

 in the haustorium under consideration become lignified, and at the 

 same time they swell up to a considerable thickness (Fig. 18), 

 until at last they come to fuse together into a yellowish mass. 

 The walls of the vessels are also disorganized into a yellowish 

 substance, which fills up the lumen of the vessels and so makes 

 the performance of their functions impossible (Fig. 17). The 

 further essential change, which takes place during the formation 

 of the duramen, consists in the disappearance of starch which 

 characterises the living cell. Thus the essential physiological 

 functions of this part, which consist in translocating and storing 

 up the nutrient substances, become entirely impossible to be 

 performed. 



It is noticeable here that the formation of the duramen in 

 the haustorium stands in close connection with the condition of 

 I lie tissue of the host-root, with which the duramen of the haus- 

 torium is connected. For, in the cases investigated, I have 

 found that, in the cross-section of the host (Abies), just under 



