18 ART. 10. — S. Kl'SANO : STUDIES OX TITE PARASITISM 



axial part, though the previous writers included this tissue in 

 thai part of the haustorium (Figs. 8, 14, 16 ca). 



The function of this cambium is of course to add the wood 

 inside and the cortex outside. Tn order that the growth in thick- 

 ness of the haustorium may go hand in hand witli that of the 

 mother-root to which it belongs, the cambium layer extends to 

 the base of the haustorium and unites witli that of the mother- 

 root, as the branch does to the stem. 



Besides, at the apex of the haustorium we find the union of 

 the cambium with that of the host which, we think, is the most 

 necessary and indispensable process. For, when two tissues of quite 

 different plants like Buchleya and its host come into intimate 

 contact and when it is necessary that a physiological communication 

 should be maintained between them, an increase of the elements 

 for enlarging the contact surface must take place at the correspond- 

 ing places in both contact surfaces in order that the danger of their 

 slipping from each other may be avoided. Accordingly if we make 

 a longitudinal section of the haustorium, which at the same time 

 cuts the host-root crosswise, we see that the cambium of the haus- 

 torium joins that of the host directly (Figs. 7, 9, 10, 11 ca). In this 

 way we can obtain in section a dumb-bell shaped circuit of the 

 cambium ring through the host, the haustorium and the mother- 

 root, whereby the elements of the haustorium are so placed, as to 

 be in the besl possible position for uniting with the corresponding 

 elements in the host- and mother-root (Figs. 7, 9, 10). 



As the cambium above mentioned serves only for the growth 

 in thickness of the haustorium we must next inquire into the 

 means of its longitudinal growth. In the primary growth we 

 have seen that the apical cells of the sucker, like all the other 

 haustoria, grow further and further in the longitudinal direction 



