66 DR. J. D. HOOKER ON THE GENERA AND SPECIES 



perianthii breviter bilabiate coronatum, 1- (rarius 2-3) loculare. Siyli 2, rariiis plures, filiformes. 

 Stigmata subcapitata, papillosa. Ovulum 1, pendulum. Fructus subcrustaceus. Semen 1, achenio 

 conforme, testa tenuissima hyalina reticulata. 



Selosis appears to be the commonest American genus of tlie Order, inhabiting both 

 sides of the Andes, and extending from Mexico to the river la Plata. The species much 

 resemble one another in general characters, and are of a whitish colour tinged with red, 

 and become red-brown when dry : they are said to inhabit moist grounds, where their 

 rhizomes spread annually by innovations to a considerable distance, seeking nourishment 

 from various roots in then progress, and seeming to have the power of attacking such as 

 they come in contact with. Each year's rhizome is probably annual, and it gives off an 

 umovation before dying, as described by Richard ; the whole mass sometimes perishes 

 at once. 



The parasitism is simply that of adhesion by the contact of the tissues of the Selosis 

 with those of the root-stock ; in the older specimens there are no vascular bundles uniting 

 both, and the roots attacked do not swell up to any remarkable size at the point of union ; 

 though the parasite often penetrates deeply into the wood by a conical protuberance. In 

 very young plants, however, the wood of the root-stock ramifies extensively through the 

 tubers of the parasite. A transverse section of the rhizome shows a most distinctly 

 exogenous structure, very curiously modified, and varying considerably in the different 

 species, under which the detaQs wiU be given which have been already referred to in the 

 general remarks on the anatomy of the Order. 



The peduncles are always erect, and rise from a swelling on the rhizome, whence they 

 receive many vascular bundles. The bundles in the peduncle are, however, simple, and 

 either promiscuously scattered, or arranged in a circle ; each resembles in structure that 

 of a monocotyledonous stem, having its own Uber, wood, and vascular portions ; but the 

 bundles do not follow the course that they do in endogenous stems, and are not to be 

 regarded as indicating any affinity between Selosis and Monocotyledons : they are, in 

 fact, solitary bimdles such as occur in the leaves, and often in the annual flowering 

 branches of other Exogens. 



An incomplete involucre, generally divided into 3-6 broadly ovate segments, is frequently 

 present in this genus ; in S. Guyanensis it is placed at the base of the peduncle, in the 

 Andes variety of that species it is carried up towards the apex, while in S. Mexicana it 

 is either reduced to an elevated ridge round the centre, or entirely absent. When fully 

 developed, this involucre never encloses the young capitulum. 



Hexagonal, peltate, fleshy scales cover the whole capitulum, as in the Indian Mhopa- 

 locnemis. In a very young state these will be found to be developed as imbricating, 

 ascending, bracteal leaves, each covering a definite portion of the inflorescence, which is 

 indicated by a vascular bundle, given off from a plexus in the body of the capitulum ; 

 then* position is hence analogous to bracts subtending branches of a flowering axis. As 

 the inflorescence grows, they become peltate, hexagonal from mutual pressure, and ad- 

 hering by their contiguous edges, fall away in large masses, leaving corresponding areolae 

 faintly marked on the capitulum. 



The male flowers have usually a conical body at the base of the tube of the perianth. 



