RHIZOGENS. 83 



CLASS III— RHIZOGENS. 



Kbizanthese, Bhm. Fl. Javce, (1828) ; Endlicher MeletemaUi, p. 10. (1832) ; Ed. prior, p. 389 ; Endl. 



Gen. p. 72. 



These are parasitical plants destitute of true leaves, in room of which 

 they have cellular scales. Their stem is either an amorphous fungous mass, 

 or a ramified mycelium, sometimes, perhaps always, appearing to be lost 

 in the tissue of the plants on which it grows; and is very imperfectly 

 supplied with spiral vessels, which in some instances seem to be wholly 

 deficient. No instance of green colour is known among them ; but they 

 are l)rown, yellow, or purple. They are furnished with true flowers, having 

 genuine stamens and carpels, and surrounded by a trimerous or penta- 

 merous calyx, or absolutely naked. Their ovules appear to be constructed 

 upon the same plan as in other floAvering plants. The true nature of their 

 seeds is in most species quite unknown ; by some they are described as 

 breaking up into a mass of spores, by others as consisting of a cellular 

 nucleus abounding in grumous corpuscles {Endl.), and in general they may 

 be regarded as too small for exact observation ; but it is certain that in 

 some instances they have a minute undivided embryo enclosed in mucilagino- 

 granular albumen. 



At this point of the Vegetable Kingdom we find a most curious assem- 

 blage, which, with many of the peculiarities of Endogens, seems to be an 

 intermediate form of organisation between them and Thallogens. They 

 have no relation to Acrogens, although they follow at this place, but they 

 agree with Endogens in the presence of sexes, and sometimes in the ternary 

 structure of their flower ; they have, however, scarcely any spiral vessels, 

 and their seeds appear, as far as they have been examined, either, as some 

 say, to want the cotyledons and axis of other flowering plants, or to lose 

 themselves in a mass of pulp, from which they are almost undistinguishable. 

 In their amorphous succulent texture, in their colour, often in their putrid 

 odour when decaying, in the formation of a mycelium or spawn, which is 

 evident in Helosis, and is with good reason suspected to exist in others, 

 and in their parasitical habits, these plants resemble Fungals, while in their 

 flowers and sexes they accord with Arumworts, or similar Endogens. 



Rhizogens all agree in being of a fungus-like consistence, and in their 

 habits of living parasitically on the roots of other plants. They very 

 generally stain water, or spirit, of a deep blood-red colour. Their forms 

 are exceedingly diversified ; some have the aspect of a Mushroom, or 

 develop a head like that of a Bullrush (Typha) : others push forth a thyrse 

 of flowers, or an elegant panicle ; while some have their bloom in a head 

 like that of some Cynaraceous plant. In Helosis and Langsdorfiia the 

 rhizome, Avhich is horizontal and branched, and which at intervals throws 

 up pci-pendicidar flowering stalks, is quite analogous to the spawn* of 



* The existence of a mycelium has also been adverted to by Dr. Brown. (Linn. Trans, xix. 232.) He 

 suggests that in Rafflesia the earliest eitbit of the seed, after being deposited in its proper nidus, may 

 consist in the formation of a cellular tissue extending laterally under the bark of the stock. He 

 remarks that in Pilostyles and Cytinus, where the plants are closely approximated, their possible ori,gin 

 from a common base or thallus,' is rendered the more probable by' the parasites in the former genus, 

 which is dioecious, being produced generally, perhaps always, in groups of the same sex, and by those 

 groups, which are often very dense, not unfrequently sun-ounding the branch of the stock. He adds, 

 however, that this view is not sustained by sufficient observation, but that there are circumstances in 

 both genera favourable to the hypothesis, especially in Pilostyles. 



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