IV. MAESILEACE^. 907 



ISTumerous observations have shown that, in most cases, Equisetums are dioecious ; 

 the prothalhis furnished with numerous and well-developed archegonia rarely hears 

 antheridia ; and if a few archegonia occur at the base of the antheridiferous pro- 

 thallus, they are nearly always sterile. This tendency to become dioecious is not 

 an obstacle to reproduction; for the proximity or overlapping of the prothalli 

 of different sexes, resulting from the entanglement of the spores by their elaters, 

 favours fertilization. Owing to this proximity, a drop of rain or dew enables the 

 antherozoids by a swimming movement to reach the orifice of the archegonium 

 which they are to fertilize. 



ONLY GENUS. 

 Equisetum. 



EquisetacecB approach Ferns in the structure of their antheridia and archegonia, as well as in their 

 mode of germination ; but as regards habit, they have no affinity with any family, unless it may be with 

 Casuaririece, with which we have compared them, or Ccdamites, which resemble gigantic Horsetails. 



The EquisetacetB now living are in general of small stature and not numerous ; the largest have 

 been met with near Caraccas by M. Ernst ; these attain about 30 feet in height. 



Horsetails principally inhabit temperate regions ; they decrease towards the pole, and are rare in 

 the tropics, and are absent throughout nearly the whole of the southern hemisphere. A remarkable 

 species (E. ramosissimum) is found in Algeria, of which the branches spread for considerable distances 

 over hedges or bushes. 



The stems of several species, being encrusted with silica, are used in the arts to polish wood and 

 even metals [and called Dutch reeds]. The rhizomes of some are starchy. J^. arvense, jlumatile, limosum, 

 and liyemale were formerly used in medicine as astringents and diuretics. 



IV. MARSILEACE^, Br., Brongn. 



Acotyledonous marsh hebbs, with a creeping rhizome. Fkonds rolled into a crozier 

 in vernation. Ertjctifioation rhizocarpian, enclosed in 2-several-celled 2-4-valved 

 sporocarps. Antheridia and spoeanGtIA enclosed in the same sporocarp, hut occupying 

 separate cells, sessile or sub-sessile on a sub-gelatinous placenta. Sporangia emitting a 

 single spore, from which springs a prothalhis bearing a single archegonium. 



Perennial plants, inhabiting swamps or inundated places. Ehizome filiform, 

 creeping and rooting ; axis composed of rayed and, annular vessels, and elongated 

 cells. Fronds radical, epidermis furnished with stomata, the extremity rolled into 

 a crozier before expansion; rachis naked [Pillularia), or terminated by 2 pairs of 

 leaflets placed crosswise. Leaflets cuneate, entire or lobed, traversed by fan- 

 shaped dichotomous nerves, and presenting, as in Oxalis, the phenomenon of 

 sleep (Marsilea). 



Fructification of two sorts, enclosed in capsular receptacles {sporocarps), solitary, 

 axillary, situated near the rhizome, or geminate, or inserted near the base or along 

 the fronds, globose or reniform, glabrous or velvety. Sporocarps 2-4-valved, 

 emitting either a mucilaginous mass which contains micro- and macro-spores mixed 

 [Pilularia), or a mucous cylinder bearing at intervals oblong sporangia which each 



