MNIADELPHACE.E. 



[ 428 ] 



MOLECULAR MOTION. 



exterior of teeth like those ofMnium, scarcely 

 lamellated, geniculately incurved when dry ; 

 interior a hyaline membrane prolonged into 

 numerous nodose filiform cilia, very much 

 appendiculated or rugulose, at first anasto- 

 mosing together, then free. 



MNIADELPHACE^E. A family of 

 Pleurocarpous Mosses, with the leaves ar- 

 ranged in four or more series, and composed 

 of parenchymatous cells, mostly equally 

 hexagonal and Mnioid, very smooth, pellu- 

 cid, destitute of a distinct primordial utricle, 

 the lowest decurrent on the stem at the base, 

 larger, spongy, lax, mostly beautifully dark- 

 tinged, never single, slender. 



British Genus. 



DALTONIA. Calyptra mitre-shaped, bell- 

 shaped, elegantly fringed at the base. 

 Peristome double (Neckeroid). External 

 sixteen narrow, subulate, trabeculate teeth, 

 reflexed when moistened ; internal : an 

 equal number of similar cilia, alternating 

 with the teeth, devoid of a basilar mem- 

 brane. 



MNIOIDEJ3. A family of operculate 

 Mosses, ordinarily of acrocarpous habit, 

 but sometimes pleurocarpous, with broadly 

 oval, spathulate, oval or lanceolate, flattish 

 leaves, having a very prominent, thick dor- 

 sal nerve. The base of the leaves composed 

 of somewhat parallelogrammic cells, rounded- 

 hexagonal or with equal walls towards the 

 apex, very full of chlorophyll, or with the 

 primordial utricle mostly very conspicuous, 

 or much thickened, firm, rarely papillose. 

 This family is divided into two tribes : 



1. MNIACEJE. Leaves without appendi- 

 cular lamellae, not sheathing at the base. 

 Capsule oval, pyriform or cylindrical, with- 

 out an annulus. 



2. POLYTRICHACE^E. Leaves mostly 

 sheathing at the base, the internal face 

 mostly lamellated ; lamellae composed of a 

 single layer of cells placed lengthwise on 

 the nerve. Capsule closed by an epiphragm, 

 without an annulus, mostly angular, apo- 

 physate, unequal. 



MNIUM, Dill. A genus of Mniaceous 

 Mosses, of acrocarpous and pleurocarpous 

 habit, including many Brya of the British 

 Flora. Among the commonest is M . hornum 

 = Bryum hornum, L. 



MOCHA STONES. The varieties of 

 chalcedony known under this name contain 

 a number of bodies which have been inter- 

 preted by authors to consist of plants, as 

 portions of Chara, Hypnum, Conferva, 



Nostoc, Desmidiacea, &c. The evidence is 

 however very unsatisfactory. 



Compare AGATE and FLINT. 



BIBL. K. Miiller, Ann. Nat. Hist. 1843, 

 xi. p. 415. 



MOHRIA, Swartz. A genus of Schizre- 

 ous Ferns. Exotic (fig. 464). 



Fig. 464. 



Mohria thurifraga. 



A pinnule with sporanges. 



Magn. 25 diams. 



MOINA, Baird. A genus of Entomo- 

 straca, of the order Cladocera, and family 

 Daphniadae. 



Char. Head rounded and obtuse; superior 

 antennae of considerable length, of one piece, 

 and arising from the front of the head near 

 the middle ; inferior antennae large, fleshy at 

 the base, and two-branched, one branch 

 three-jointed, the other four-jointed; legs 

 five pairs. 



M. rectiroslris (PI. 14. fig. 26). Carapace 

 almost straight or but slightly rounded be- 

 hind. Aquatic. 



M. brachiata or branchiata. Carapace 

 greatly rounded behind. Aquatic. 



BIBL. Baird, Brit. Entomos. p. 100. 



MOLECULAR MOTION. When ex- 

 tremely minute particles of any substance 

 immersed in water or other liquid are exa- 

 mined under the microscope, they are seen 

 to be in a state of vivid motion. A little 

 gamboge or Indian ink mixed with water 

 will exhibit the phaenomenon distinctly 

 enough. The minute particles or molecules 

 are seen to move irregularly, to the right 

 and left, backwards and forwards, as if re- 

 pelled by each other, until the attraction of 

 gravitation ultimately overcomes the force 

 upon which their motion depends, when 

 they sink to the surface of the slide. This 

 applies to the molecules of those substances 

 which are heavier than water. In the case 

 of those which are lighter than water, or the 

 liquid in which they are immersed, the mole- 



