256 



ABSORBING SYSTEM 



vessels of the primary hadrome groups, to which they become closely 

 attached (Fig. 102 a). Others force their way between the primary 

 bundles [on the opposite side of the pith], and for the second time 

 break through the feebly developed mechanical tissue ; in this way 

 they reach the primary and secondary leptome, where they produce 

 irregular lobed expansions (Fig. 102 b). The majority of the tubes, 

 however which all contain abundant protoplasm and large nuclei 



Fio. 102. 



Haustorial tubes of Cuscuta europaea. A. Tracheidal haustorial tube which has 

 attached itself to a hadrome -strand of the host-stem (Urtica dioica), after traversing 

 the pith. Its walls are lignified throughout, and (towards the branched distal 

 end) provided with scalariform or reticulate thickenings. One of the terminal 

 branches is in immediate contact with a protohadrome element ; the other is separated 

 from the wood-vessels by a layer of hadrome-parenchyma cells, the walls of which are 

 swelling. B. Haustorial tube which has penetrated to the leptome of the host-stem 

 (Urtica dioica), after traversing the pith and breaking through the cylinder of wood- 

 fibres ; the expanded and irregularly lobed distal extremity of the tube contains 

 abundant cytoplasm and a nucleus. 



remain in the pith, which they traverse in all directions. The 

 haustoria of C. epithymum behave in a very similar fashion. 



Among the most remarkable of all Phanerogamic parasites are the 

 PtAFFLESiACEAE, to which reference has already been made. While the 

 flowers of the genus Rajjiesia, as is well known, reach gigantic 

 dimensions, there is in these plants not the slightest trace of stem, 

 leaf or root, or indeed of any vegetative organs of the ordinary type. 

 The plant-body is, in fact, represented by a thcdlus, composed of 

 numerous branching cellular strands, which is quite comparable to the 



