MUSCALES.] 



EQUISETACE/E. 



Gl 



Order XVIII. EQUISETACEiE.— Horsetails. 



Equisetaceas, DC. Fl. Fr. 2. 580. (1805); Agardh Aph. 119. (1822); Kaul/uss Enum. Filicum, l. 

 (1824) ; Adolphe Brongniart Hist. Veg. Foss. 99. (\9,2B.)—E)idl. Gen. xxv. Linkfilic. sp. p. 9. 



Diagnosis. — Spore-cctses peltate^ splitting on one side, without operculum, and with an 

 elater to ever 7/ spore. 



Leafless branched plants with a striated fistular stem, in the cuticle of which silex is 

 secreted ; the articulations separable and surrounded by a membranous toothed sheath. 

 Stem fistular, with many longitudinal caA-ities in its circum- 

 ference ; chiefly consisting of cellular substance, but coated 

 externally with a layer of hard woody tubes, from which plates 

 of a similar nature project towards the centre, partially divid- 

 ing the longitudinal cavities from each other. Stomates ar- 

 ranged longitudinally on the cuticle. Spiral vessels very small 

 but abundant. Spore-cases opening inwards by a longitudinal 

 slit, attached to the lower face of peltate scales, which are col- 

 lected into tei'minal cones. Spores, oval grains, wrapped round 

 with a pau" of highly elastic clavate elatei-s. 



The remarkable plants kno\\Ti by the vulgar name of Horse- 

 tails, seem to have no very decided affinity to any existing 

 order. With Ferns their relation is not ob\'ious. In the ar- 

 rangement of their reproductive organs they have a striking 

 resemblance to Zamia, and in their general aspect to Ephedra or 

 Casuarina. Then' germmation is that of Cellular plants, and 

 approaches nearly to Urnmosses. The structm*e of their stem 

 is well described by Ad. Brongniart in his Histonj of Fossil 

 Vegetables, as are, indeed, other parts of then' organisation : see 

 Tables, 11 and 12 of that work. This ingenious writer enter- 

 tains the opuiion that the green body, which is known to be the 

 spore, is a naked OAiile, and the four swollen filaments that sur- 

 round it fom' grains of pollen united in pairs to the base of the 

 o\Tile. In the last edition of this work I adopted M. Brongniart's 

 Adew, and accordingly placed Equisetum with Coniferae, an error 

 so very obvious, as to have called forth rebukes, which were 

 richly deserved. The development of the swollen filaments has 

 been carefully observed by Mohl, Henderson, and others, who 

 have demonstrated that they are really produced by the spiral 



splittmg of the cell in which the spore is fonned ; in fact, they appear quite analogous, 

 as ^Ir. Griffith has stated, to the elaters of jNIarchantia and its allies, to which the order 

 bears, perhaps, a nearer relation than to any other plant. To regard Horsetails as a high 

 form of the Muscal alhance seems to me more 

 expedient than to station them with Ferns and 

 Clubmosses, to which they seem to have no 

 immediate affinity. The resemblance between 

 the peltate scales of Equisetmn and the heads 

 of spore-cases in Marchantia, is too obvious not 

 to strike the most impractised observer. Link 

 calls these scales Sporidochia. 



The germination of the spores has been ex- 

 plained, both by Agardh and Bischoff". The 

 former {Aphor. 120) describes it thus : from 

 three to fourteen days after they are sown, they send do\\ni a filifoi-m, hyaline, some- 

 what clavate, simple root, and protrude a confervoid, cyUndrical, obtuse, articulated, 

 torulose thread, either two-lobed (in E. pratense) at the apex, or simi)le (in E. palustre). 

 Some days after, several branches grow out and are agglutinated together, fomiing a 

 body resembling a bundle of confervoid threads, each of which pushes out its own root. 

 The account of Bischoff" {Nov. Act. Acad. N. Cur. 14. t. 44.) is not materially diff'erent : 

 he finds the confervoid threads, or numerous processes of cellular development, go on 



XLII. 



-sr3 



Fig. XLIII. 



Fig. XLII.- 

 Fig. XLIII. 



-Equisetum an'ense. 1. A peltate disk seen from the side. 

 —Equisetum ; its spores wrapped round by elaters. 



