GROUP II. BRYOPHYTA : HEPATIC JE. 329 



Sphserocarpus), are marked out by four longitudinal rows of small-celled 

 tissue which correspond in position with the walls between the four apical 

 cells of the growing embryo. 



The archesporium, which is co-extensive with the endothecium, presents 

 various degrees and forms of differentiation. In the Riellese it comes to 

 consist of a number of cubical cells, some of which become the mother- 

 cells of the spores, whereas the others persist as unaltered sterile cells. 

 In all the other Jungermanniacese &ome of the cells of the endothecium 

 are sterile, but they develope into elaters, becoming elongated in form 

 and spirally thickened, having sometimes two spirals, or only one. The 

 relative arrangement of the sterile and fertile cells, dependent upon the 

 growth of the capsule along different diameters, varies somewhat. In the 

 lower forms, the elongated archesphorial cells are arranged more or less 

 longitudinally, either quite straight (e.g. Frullania, Lejeunia), or radia- 

 ting from the apex of the capsule (Metzgeria, Aneura), or radiating from 

 the base of the capsule (Pellia, Badula): whereas in the higher forms 

 (Lepidozia, Calypogeia, Jungermannia), these cells are placed horizontally 

 round a central longitudinal axis, except at the apex where they radiate. 

 In most cases the sterile and fertile archesporial cells are mingled to- 

 gether, but in some cases certain parts of the archesporium give rise 

 especially to spores and others to elaters. Thus, in Pellia, the cells to- 

 wards the base and those in the longitudinal axis of the capsule form 

 only elaters, whereas in Jungermannia the formation of elaters is confined 

 to the cells near to the wall. 



Whilst the development of the embryo is taking place, growth is also 

 proceeding in the archegonium and the adjacent tissue, giving rise even- 

 tually to the calyptra. Several of the archegonia of a group may be 

 fertilised, but generally only one gives rise to a fully developed sporo- 

 gonium, and itself takes part in the formation of the calyptra. The 

 calyptra is sometimes developed from the venter of the archegonium 

 alone (e.g. generally in the Acrogynae) ; in the Anacrogynae the adjacent 

 tissue of the shoot frequently takes part in its formation, as is shown by 

 the fact that the unfertilised archegonia of the original group are found 

 on the sides, or even on the top of the calyptra (e.g. Aneura, Pellia). The 

 wall of the calyptra consists of one or more layers of cells, and keeps pace 

 with the growth of the embryo which it encloses until the spores are mature. 

 The cells of the seta then rapidly elongate, causing the rupture of the 

 calyptra, and the capsule is exposed. The capsule then dehisces, 

 generally into four valves, sometimes irregularly, and the spore* are 

 set free. 



The Jungermanniaceae may be classified as follows : 



Series I. ANACROGYX.E : growth in length not necessarily arrested by 



the development of archegonia. 

 Section A. Anelatereae : the sterile cells in the capsule do not 



develope into elaters. 



This section consists of the family Riellece: including the two 

 genera Kiella (foliose) and Sphaerocarpus (thalloid). 



