320 PART IV. CLASSIFICATION. 



sterile, and in many they are developed into elatcrs, elongated 

 cells with spirally thickened walls, generally becoming free from 

 each other. 



The sporogonium remains enclosed in the calyptra until the 

 spores are mature when, if a seta be present, it suddenly elongates 

 and ruptures the calyptra, which persists as a vaginula at its base. 

 The capsule opens either by the decay of its wall, or more gener- 

 ally by the splitting of the wall from the apex downwards into 

 valves ; in some Marchantiese a lid, the operculum, is formed and 

 the capsule is opened by the throwing off of the lid. 



The Hepaticse are classified as follows : 



Order I. Marchantiacese. Order II. Jungermanniacese. Order III. 

 Anthocerotacese. 



Order I. Marchantiaceae. 



A. The GAMETOPHYTE. The spore gives rise on germination to a short 

 unbranched filamentous protonema which developes at its apex into a 

 flattened cellular expansion, from the margin of which the adult shoot 

 (commonly known as the plant) springs as a lateral branch. 



The Morphology of the Adult Shoot. The adult shoot is undiiferentiated 

 into stem and leaf. Its symmetry is dorsiventral ; on the lower (ventral) 

 surface it bears numerous root-hairs, and also scales which are arranged 

 in one or two rows, or irregularly. 



Growth is effected by an apical growing-point, situated in a depression, 

 possessing a transverse row of initial cells from which segments are cut 

 off dorsally and ventrally; the initial cells also undergo longitudinal 

 division, and thus increase in number. 



The normal mode of branching is that which takes place in the plane 

 of expansion; it is dichotomous, and is effected in the manner described 

 on p. 132. 



The sexual organs are in all cases developed on the dorsal surface, each 

 antheridium or archegonium arising from a single superficial cell. In 

 the simpler forms they are arranged in a continuous median row, 

 developed in acropetal succession ; in the higher forms they are borne on 

 a special structure termed a receptacle. 



The receptac'e. In the higher Marchantiese the adult shoot is frequently 

 differentiated into a vegetative and a reproductive portion, the gameto- 

 phore; the gametophore is a branch (or a branch-system) bearing a 

 terminal receptacle, in which either the male (antheridiophore) or the 

 female (archegoniophore) organs are developed. 



In the simpler forms the archegoniophore is simple, that is unbranched ; 

 the stalk presents a single furrow which represents the ventral surface of 

 the shoot. In Marchantia the stalk has two ventral furrows, showing 

 that it consists of the two coherent branches of the first dichotomy. The 

 receptacle itself is repeatedly branched: thus in Marchantia there are 

 eight groups of archegonia, corresponding to eight branches. The 

 receptacle is more or less distinctly lobed, thus showing its compound 



