384 PRIMARY ARRANGEMENT OF TISSUES. 



the sucker. The vessels of the strands consist, in all these haustoria, of short 

 elements communicating by wide perforations ; in the sucker they are usually more 

 elongated, the reticulate, thickenings of their membranes being often imperfectly 

 developed at the surface of the process. 



(2) The intramatrical ramifications of the haustorium of Viscum and Phora- 

 dendron, which have been described as cortical roots, are traversed by an irregular 

 axial vascular strand, which ends in the apical meristem, and is developed slowly and 

 relatively late. In the ' borers,' which, starting from the cortical root, penetrate the 

 wood of the host, like wedges, the middle is occupied by a relatively thick mass of 

 vessels, the remainder of the body consisting of large-celled parenchyma. The 

 vessels do not reach the edge of the borer. 



In the broader outer portion, the bundle is irregularly branched, and from the 

 branches numerous vessels with short elements run generally with a curved course 

 towards the lateral surfaces of the borer, and here attach themselves to the elements 

 of the wood of the host. In very old borers, which have finished their growth, the 

 vessels are continuous with those of the cortical root. So long, however, as the 

 borer is still growing, they are separated by a zone of meristem, which cai-ries on 

 the growth, and lies in the cambium of the wood of the host (Chap. XIV). The 

 vascular body of the borer may be massively developed, while as yet no vessels have 

 been fully formed at its point of origin in the cortical root. Arceuthobium Oxycedri, 

 which is much smaller in all its parts, has no vessels at all in the smaller branches of 

 its cortical roots, or in its small ' narrow ' borers ; the latter simply consist of a few 

 rows of large parenchymatous cells. The thicker cortical roots and borers are 

 similar in structure to those of Viscum album, but are simpler, as corresponds to 

 their small bulk. Similar conditions to those in Arceuthobium recur in the intra- 

 matrical thallus of Pilostyles, with specific variations. 



(3) The flat intramatrical body of Cyiinus Hypocistis (cf. Graf Solms, I.e., 

 Taf. 36, 37), which is irregularly discoid, and on its lower surface wedged with 

 irregular protrusions into the wood of the host, is traversed throughout by isolated, 

 very irregular vessels, which are abundantly branched and reticulately connected, and 

 which in the wedged protrusions are attached to the ligneous elements of the host. 

 The elements of the vessels are as a rule irregularly rounded, with a reticulated wall, 

 and are in communication by means of large round holes. 



(4) In the tuberous regions of attachment of the Orobanches, the vascular 

 bundles, both of the parasite and of the host-root bearing it, are as it were broken 

 up into a loose web of numerous vessels with short elements, those of the parasite 

 standing in immediate continuity with those of the host. A sharp boundary, whether 

 between the vessels or between the parenchyma of host and parasite, is often only to 

 be recognised in the youngest stages ^. 



In the tuberous regions of attachment of most genera of Balanophorese (Helosis, 

 Lophophytum, Scybalium^), the conditions of structure are similar to those in 

 Orobanche, except that the vessels are clearly distinguishable from those of the woo4 

 of the host-root, as far as the point of attachment to the latter. Essentially the same 

 holds good of the Rafiflesiacese. 



1 Caspary, Flora, 1854, Taf. III. " Eichler, BalanophorjE biasilienses, I.e. (p. 254). 



