HEPATICACE.E. [ 319 ] HEPATICACE^. 



meet, if prolonged across the stem, in the 

 form of a V (fig. 324). 



The leaves are very frequently imbricated, 

 and they overlap in two ways : either each 

 leaf covers with its lower edge a little of the 

 leaf below it, or each leaf overlaps a little of 

 the base of the leaf above it. In the first 

 case, the leaves are called succubous (fig. 

 324), in the second, incubous (fig. 325). The 

 leaves vary much in form, and are often 

 deeply toothed or bilobed, and form exceed- 



Fig. 324. Fig. 325. 



thickness and a complexity of internal struc- 

 ture, since it possesses an epidermis invest- 

 ing both surfaces, and containing stomates 

 on the upper (see STOMATES). The lower 

 epidermis is also provided with numerous 

 radical hairs (see HAIRS and SPIRAL STRUC- 

 TURES). Fimbriaria (fig. 322), Lunularia 

 (fig. 323), &c., likewise possess thick cellular 

 fronds. In Riccia the frond also presents 

 a reticulated upper face provided with sto- 



Fig. 323. 



*%* 



Lunularia vulgaris. 

 A frond in fruit. Nat. size. 



mates, but the form of the entire frond is 

 usually elongated and bifurcated, and a slight 

 groove runs along the middle line, almost 

 like a mid-nerve. This central line exhibits 

 a difference in the internal cellular structure, 

 since it is composed of elongated cells, while 

 the surrounding green substance is composed 

 of spherical cells, such as constitute the en- 

 tire mass enclosed between the upper and 

 lower epidermis of the frond of Marchantia. 

 The groove on the upper face (of Riccia) 

 corresponds to a rib on the lower face, from 

 which arise most of the radical filaments, 

 while they are scattered indiscriminately 

 over the lower face of Marchantia; and 

 from this line also arise the little bodies re- 

 sembling minute leaves, called amphigastres. 

 If we suppose the frond of Riccia elongated 

 and the mid-nerve more strongly marked, 

 we have the likeness of Bfytia Lyellii (fig. 

 63, p. 87) ; while if this latter were notched 

 down to the rib at intervals along each side, 

 we should have the stem with two parallel 

 rows of leaves, as in the Jungennanniese. 



The line of insertion of the leaves is sel- 

 dom exactly parallel with the axis of the 

 plant, and very rarely at right angles. In 

 most cases it is more or less oblique, and 

 the obliquity is in reverse direction at the 

 two sides of the stem, so that the lines of 

 insertion of two succeeding leaves would 



Fig. 324. Radula complanata. Magn. 5 diams. 

 Fig. 325. Plagiochila undulata. Magn. 5 diams. 



ingly elegant objects under the microscope. 

 The leaves are accompanied in many cases, 

 chiefly in the Jungermannieae, by stipule-like 

 leaflets, called amphigastres, situated at the 

 under side of the stem. 



These plants are reproduced by dust-like 

 grains called spores, by minute cellular no- 

 dules called gemmce, and by innovations, i. e. 

 new lobes growing out from the margins of 

 the old fronds, or buds in the axils of leaves, 

 or on confervoid branches sent out from the 

 stem. 



The gemmce of Marchantia polymorpha are 

 produced in elegant membranous cups, with 

 a toothed margin, growing on the upper 

 surface of the frond, especially in very damp 

 and imperfectly lighted situations ; they are 

 little cellular nodules at first attached by a 

 stalk, and at a certain period fall off and 

 grow up into a new frond. (See MARCHAN- 

 TIA.) 



The spores are produced in sporanges or 

 capsules, the formation of which is preceded 

 by special anatomical and physiological phae- 

 nomena demonstrating the existence of di- 

 stinct sexes in these plants. The organs 



