86 RHIZOGENS. 



p. 23.) Endliclier describes the seeds of Scybalium fimgiforme as being a 



"nucleus compositus e tela cellulosa, corpusculis sporidiiformibus e cellulis 



anffiilatis conflatis et massulis oTumosis immixtis, filis tenuissimis earmidem 



... 

 particulas connectentibus farcta." But these are perhaps mistakes arising 



from inaccurate observation. At least I can positively confirm the state- 

 ment of the elder Richard [Mem. Mus. viii. t. xxi.), who gives to Cjno- 

 morium coccineum an embryo. I find in that plant that the seed consists 

 of a mucilaginous mass filled with angular particles, which are doubtless 

 loosely cohering cells. They contain starch in a very minutely globular 

 state, but are chiefly composed of gum. On one side of this seed is a 

 globular embryo, looking like a speck, but found, when properly examined, 

 to be a globose mass of cells, destitute of starch, enclosed within the 

 albumen, and apparently undivided on any part of its surface. It is, 

 however, difficult to speak positively upon this point, on account of its small- 

 ness, and I am not sure that it is not very slightly 2-lobed. Francis Bauer 

 too ascertained the ovules of liafflesia Arnoldi to have the ordinary struc- 

 ture, a strong indication that the seeds would not be so anomalous as has 

 been represented, and he found an undivided embryo in the seed of the 

 same plant, [Linn. Trans, xix. t. xxv.) a circumstance confirmed by the 

 observations of Brown. Ferdinand Bauer, too, found in Hydnora Africana 

 what seems to be a central embryo [Ibid. t. xxx.) of the same nature. 



Such being the principal facts that have been ascertained with regard to 

 these singular parasites, it only remains to notice some of the views enter- 

 tained regarding them by systematic botanists. Dr. Robert Brown, who, 

 aided by the microscopical drawings of the two Bauers, has had peculiar 

 advantages for considering the question, appears to be opposed to the idea 

 of regarding Rhizogens as a peculiar class. He considers the Patma worts 

 (Rafflesiacese) as being unquestionably allied to Birthworts, and therefore 

 as a form of Exogens. The reasons, however, which have led this botanist 

 to form such an opinion, require to be stated with much more detail before 

 they can claim serious attention. His objections to regarding Rhizogens 

 as a peculiar class are more definite. 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 Rhizo- 

 gens is not essentially difierent from that of any perfectly developed Phseno- 

 gamous 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 fohaceous 

 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 Clubmosses, 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- 



