Uli ART. 10. — S. KUSANO : STUDIES ON THE PARASITISM 



being very serviceable for the function of the haustorium. Fur 

 in order to assume an intimate union of the elements between the 

 host and the haustorium, it is evident that the growth in thick- 

 ness of the latter must go on parallel with that of the host (i. c. 

 in the direction of wz, Woodcut 1). But a« no secondary longi- 

 tudinal growth occurs in the host, there is needed in the haus- 

 torium no remarkable growth in the direction of the axis of the 

 host (Woodcut 1, xy). 



The natural consequence of such secondary growth in thick- 

 ness especially in a lateral direction, unaccompanied by longi- 

 tudinal growth, is that the axial part is reduced to a disc with 

 varions outlines, according to its age as well as to the proportion 

 of its height to its breadth. In all haustoria, especially in old 

 ones, the vascular strand has the concave bottom (Figs. 9, 10) 

 and also in some vigorously growing haustoria, as, for instance, 

 those which feed on Abies, the frontal portion of the strand 

 is likewise concave (Fig. 9). So, if the haustorium is pretty old 

 the axial part will take the form of a biconcave lens, or if it 

 is somewhat younger it will assume the form of an amphiccelous 

 vertebral bone (Fig. 9). In a less vigorous haustorium the front, 

 being overlapped by the tissue of the host on account of the very 

 vigorous growth of the latter, becomes convex and then the axial 

 part assumes the form of an opistoccelous vertebral bone (Fig. 

 10). Not only are all these forms to be seen in sections, but 

 also not infrequently they may be found even on the dead haus- 

 toria still resting upon the host ; in this case, however, the 

 cortical parenchyma having already decayed, only the hard 

 lignilied axis with concave base is barely exposed (Fig. 6 Ju\). 



