86 RHIZOGENS. 



He denies the absence of spiral vessels, which he himself and others once 

 supposed to be a characteristic of some at least among them, and asserts 

 that the vascular texture of Rhizogens is not essentially different from that 

 of any perfectly developed Phscnogamous plants. But, as was stated in 

 the last edition of this work, the true question to be considered is, not as to 

 the presence or absence of spiral vessels, but as to their abundance. In 

 Exogens or Endogens equally developed they would be most copious, and 

 would exist in all the foliaceous organs ; and it is no argument against the 

 importance of this circumstance, to say, that spiral vessels have no existence 

 in certain Endogens, as Lemna, for instance ; for in that and similar cases 

 the small degree in which such plants are developed, may be considered to 

 account for the absence of spiral vessels ; just as in a common Exogen, the 

 spiral system does not make its appearance until the general development 

 of the individual has made some progress. 



So, indeed, in Ferns and other Acrogens of high degree, we have no 

 right to say that the vascular system is absent ; on the contrary, in the 

 centre of the stem of Ciubmosses, and in the soft parts of that of Ferns, 

 either spiral or scalariform vessels exist in abundance ; but they do not 

 make their appearance in the foliaceous organs as in more perfect plants. 



Brown also attaches no importance to the supposed homogeneity of the 

 embryo of Rhizogens, because the same structure, he says, exists in Oro- 

 banche and Orchids. But with regard to Orobanche, that plant has a 

 slightly two-lobed embr} r o lying in a mass of albumen, so that I do not see 

 how it can be brought into comparison with that of Rhizogens ; and as to 

 Orchids we have no right to say that their embryo is essentially different 

 from that of common Endogens, except in its smallness. 



The late Mr. Griffith adopted the views of Brown, and endeavoured, by 

 new arguments, to show that Rhizogens cannot be regarded as a peculiar 

 class in the Vegetable Kingdom. He asserted that these plants are not 

 similar in their parasitism, and that in those he had examined there would 

 appear to be two remarkably different types of development of the embryo. 

 And he was persuaded that Rhizogens are an entirely artificial class, not 

 even sanctioned by practical facility. — (Proceedings of the Linnean Society, 

 No. XXII. , p. 220., where this author's views are given in detail.) 



Arguments like those of both Brown and Griffith never appeared satis- 

 factory to me. Most of the species brought together to constitute the class 

 of Rhizogens seem to have little relation to other parts of the system. It is 

 true that the genera differ much from each other in the details of their 

 fructification ; though not more than the genera of some other classes ; but the 

 character of the order does not depend upon the fructification. It depends upon 

 the great peculiarity iu the manner of growth, already pointed out; and 

 the fructification is connected with questions of a subordinate degree. All 

 the classes of plants depend equally upon such considerations ; and, there- 

 fore, Rhizogens are logically a class. It was indeed singular that so acute 

 a botanist as Griffith should not have perceived how much his position was 

 weakened by comparisons like the following. He particularly directed 

 attention to the resemblance between the pistil of Balanophorads and that 

 of Mosses, or more especially to that of some evaginulate Liverworts, and to 

 the effects produced by the action of the pollen on their styles. " Indeed," 

 he observed, "in the development of the female organ, in the continuous 

 surface of the style before fecundation, and in its obvious perforation after, 

 Balanophora presents a direct affinity to a group of plants with which other- 

 wise it has not a single analogy." In another genus, called Phseocordylis, 



