8 DR. J. D. HOOKER ON THE STRUCTURE AND 
of having ascended from it, instead of having descended to it. This union once established, 
the difficulty of regarding the vascular bundles as originating in the parasite and drawing 
their nourishment 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 great 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 surrounded by a cortical layer (Plate VIII. figs. 10, 3 
llo) It must however be borne in mind, that there is no law more universal in the 1 
vegetable kingdom than that vascular tissue is developed according to the requirements | 
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 organie 
cohesion between their respective vascular systems. As the rhizome increases, the 
organic cellular cohesion extends with the increased surfaces of the parasite and root, by 
the merismatie subdivision of the cells of both; and the vascular system increases by the 
development of pleurenchyma, ducts, &e. from those nucleated cells which are found in 
the positions in which vessels are required. 
- In a case of parasitism like that of Balanophora, which involves perfect organic cohesion « 
between the individual cells of different plants, it must obviously in many instances be 1 
impossible to draw the line between the tissues of the parasite and those of the root on 1 
which it grows. With regard to the cellular tissues, however, there is generally no diffi- 3 
culty; for, that of the Balamophora containing organie compounds (wax), the line of 1 
union is evident; but it is different with the vascular systems, which consist in both cases 4 
of tubes of indefinite length, containing no solid organized contents, and presenting an q 
extreme simplicity of form. Again, granting (as we must) that in Lophophytum (and in | 
Scybalium, 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 funda- 1 
mentally distinct principles of development amongst very closely allied species ; namely, that 3 
the germinating plant of some does form. independent vascular bundles (in common with all . 
Phænogamic 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 Langsdorfia, 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 
ea da ne inc 
