20 AIIT. 10. — S. KUSANO : STUDIES ON THE PARASITISM 



It has already been noticed that, on either transverse or longi- 

 tudinal sections, vessels are arranged irregularly at the base as 

 well as the inner region of the strand, and are short and irregular 

 in form, while in the remaining part each succeeding prismatic 

 vessel is so placed that the result is a radial row. It seems 

 beyond doubt that the irregularity of the arrangement of the 

 innermost vessels is due to their origin from the procambial cell- 

 groups, directly differentiated in their own form just as we see in 

 the formation of the primary wood in the fihro-vascular bundle. 

 But immediately after the complete formation of the cambium 

 ring, secondary elements being derived from the latter by its 

 tangential division will be arranged in radial rows. 



At the earlier period of growth, rows of vessels are directed 

 laterally, being all approximately parallel, even at the extremities 

 of both strands (Fig. 8). But as the activity of the cambium is 

 greater laterally (i. e. in the direction of wz t Woodcut 1) than in 

 the direction perpendicular to it {i.e. in the direction of xy), the 

 diameter of the axial part increases greatly in the former direction 

 and the rows of vessels derived henceforth begin to diverge from 

 one another, and when the cambium becomes circular, they become 

 radially arranged. The formation of vessels from the cambium 

 being always strongest in the lateral direction, the vascular strand 

 which has once become circular will then become longer laterally 

 and take in section an elliptical shape with its minor axis placed 

 in the direction of the major axis of the primary ellipse. 



The diagram here given will demonstrate the modification of 

 the form of the axial part during its secondary growth (Woodcut 

 1). It indicates three types of form in cross-section, which the 



]). As far us my observation goes pretty uld haustoria mostly keep thi^ fuim 



