26 ART. 10. — S. KTJ8ANO : STUDIES ON THE PARASITISM 



radially, is completed. The cells of the medullary rays are usually 

 rectangularly prismatic, often with rounded corners, somewhat 

 comparable to bricks, for they chiefly elongate in one direction 

 and lie with their greatest diameter directed horizontally and 

 radially. The form of rays can be learned from the sections of 

 the haustorium in its transverse, longitudinal and tangential 

 directions : they are flat bands, like ordinary rays, composed of 

 many layers of cells transversely, but only a few layers thick 

 (Fig. 10). They occur pretty abundantly ; some originate from 

 the pith and traverse the thick bundle of vessels, while others 

 take their start in the bundle itself and proceed toward the cortical 

 part, Even in older haustoria the wall of the cells remains 

 unlignified, delicate, and capable of yielding to pressure and 

 tension, 1 ' so that they are often laterally compressed, sometimes 

 with abundant reserve starch (Fig. 16. a). 



We may ask then how the medullary rays behave themselves 

 when they enter the cortical part. When they penetrate the 

 cambium layer and run among the cortical parenchyma, they are 

 difficult to be distinguished, their structure being similar to that 

 of the crrtical parenchyma, Their outer form and the direction 

 of their longer axis alone serve for their distinction (Fig. 15). 

 Not infrequently does it happen that in cross-section both elements 

 are so similar in their form that they are hardly distinguishable 

 from each other, but in radial section the medullary rays can 

 always be plainly recognized as such by their horizontal course, 

 the axis being elongated in this direction, while the cortical 

 parenchyma runs longitudinally. 



Having thus ascertained the existence and distribution of the 



1). For the sake of comparison I have examined the medullary rays in the wood of the 

 mother-root. The cell-wall is lignified and thickened, having numerous pits. 



