OF BUCKLEYA QÜADKIAtiA, B. ET H. 19 



dividing themselves transversely, and after penetrating the cortex 

 of the host, come into contact with the wood tissue. The primary 

 growth of the haustorium seems generally to be arrested, when its 

 apex thus reaches the ligniiied cells of the wood, since, they are 

 so hard and so thick that they can resist against the penetration 

 of the young thin-walled apical cells of the sucker. Only rarely 

 some few apical cells can penetrate further into the wood tissue 

 of the host, compressing in their course the ligniiied cells of less 

 resistance, as, for instance, the medullary rays. But this local 

 and limited prolongation is not to be considered as a longitudinal 

 growth of the whole sucker. 



Again we have ascertained very frequently that when the 

 haustorium occurs on a young host-root in the first year of its 

 development, the penetration and longitudinal growth of the sucker 

 do not cease at the cambium zone of the host, but on the other 

 hand as the tissue at this stage is still soft and thin walled the 

 sucker easily makes its way further in. 



Manifestly the parenchyma will be least resistent against the 

 pressure exerted by the forward growth of the haustorium as well as 

 the chemical action of the same. 1 * So the sucker grows in this direc- 

 tion, dissolving and pushing aside and exending itself to the pith. 



As the apical cells of the sucker, after the primary growth, 

 become the permanent tissue, the occurence of the secondary 

 growth will become impossible. 



2. The Vascular Strands. 



Having determined the occurence of the cambium laver and 

 its distribution, we shall now study the vessels derived from it. 



1). The action of the haustorium upon the host is worthy a special treatment which 

 will he given in future. 



