8 DR. J. D. HOOKER ON THE STRUCTURE AND 



of lla^-in"■ ascended from it, instead of having descended to it. Tliis union once established, 

 the difiicnltv of regarding the vascular bundles as originating in the parasite and drawing 

 theii- nom-ishinent from the root, appears to me less than that of regarding them as 

 dependent both for origin and increase upon a reversed and diseased action of the root. 

 The oTcat theoretical objection to this view is, that the anatomical characters of the vas- 

 cular bundles of the parasite precisely resemble those of the root, and that in some species 

 they are even found to arrange themselves in the forms of woody plates and medullary 

 rays, enclosing a pith axis, and to be sm-rounded by a cortical layer (Plate VIII. figs. 10, 

 11 a). It must however be borne in mind, that there is no law more universal in the 

 vegetable kingdom than that vascular tissue is developed according to the reqviirements 

 of the plant, both as to abundance and kind ; and that the formation of a perfect organic 

 cohesion between the walls of the individual cells of the cellular systems of the parasite 

 and root, is in no respect less anomalous than the similar perfect and intimate organic 

 cohesion between their respective vascrdar systems. As the rhizome increases, the 

 organic cellular cohesion extends with the increased surfaces of the parasite and root, by 

 the merismatic subdivision of the cells of both ; and the vascular system increases by the 

 development of pleurenchyma, ducts, &c. from those nucleated cells which are found in 

 the positions in which vessels are required. 



In a case of parasitism like that oi Balanophora, which involves perfect organic cohesion 

 between the individual cells of different plants, it must obviously in many instances be 

 impossible to draw the line between the tissues of the parasite and those of the root on 

 which it grows. With regard to the cellular tissues, however, there is generally no diffi- 

 culty; for, that of the Balanophora containing organic compounds (wax), the line of 

 union is evident ; biit it is different with the vascular systems, which consist in both cases 

 of tubes of indefinite length, containing no solid organized contents, and presenting an 

 extreme simplicity of form. Again, granting (as we must) that in Lophophytum (and in 

 Scyballmn, according to Unger's observations) the vascular tissue of the rhizome never 

 descends to that of the root, and hence cannot form an organic cohesion with the latter, we 

 must assume an independent origin for it in these genera, at any rate ; the application of 

 which to Goeppert's views involves the necessity of concluding that there are two fim.da- 

 mentally distinct principles of development amongst very closely allied species ; namely, that 

 the germinating plant of some does form independent vascular bundles (in common with all 

 Phsenogamic plants), but that that of others does not. To me it appears more in accord- 

 ance with the known laws of development, to suppose that the origin of the vascular 

 system is the same in both, but that its after- development is modified in different cases. 



In Langsdorffia, where the rhizome has certainly a highly developed vascular tissue of 

 its own, and where the root also appears to send branches into the rhizome, although I 

 have never found the vascular system of the latter to unite with that of the root, I can- 

 not but admit that such a union may exist, for the difficulty of dissecting the mixed brittle, 

 woody, and flaccid tissues of this plant is very great. 



The last argument which I shall bring forward in favour of considering the vascular 

 system of the rhizome as in its origin proper to the parasite, is derived from the fact of 

 free vascular bundles being formed in the flower-buds or nascent peduncles ; which is 



