GROUP II. BEYOPHYTA : HEPATIC^E. 351 



Aneura, Metzgeria). The relative arrangement ofithe sterile and fertile ceils, de- 

 pendent upon the growth of the capsule along different diameters, varies some- 

 what. In the lower forms, the elongated archesphorial cells are arranged more or 

 less longitudinally, either quite straight (e.g. Frullauia, Lejeunia, Symphogyna, 

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

 or radiating from the base of the capsule (Pellia, Eadula) : whereas in the 

 higher forms (Lepidozia, Calypogeia, Jungermaunia), 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 

 together, but in some cases certain parts of the archesporium give rise especi- 

 ally to epores and others to elaters. Thus, in Pellia, the cells towards the base 

 and those in the longitudinal axis of the capsule form only elaters, whereas in 

 Jnngermannia 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 pro- 

 ceeding in the archegonium and the adjacent tissue, giving rise eventually to 

 the calyptra. Several of the archegonia of a group may be fertilised, but 

 generally only one gives rise to a fully developed sporogonium, 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 Acrogynaa, and 

 in Metzgeria, Fossouibronia) ; in the Anacrogynas 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, Svmphogyna). The wall of the catyptra 

 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, eometimes 

 irregularly, and the spores are set free. 



The Jungermanniacea3 may be classified as follows : 



Series I. ANA.CROGYN;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. 



Fam. 1. Riellete : including the two genera Kiella (foliose) and 

 Sphaerocarpus (thalloid) ; further characterised by the 

 absence of annular thickenings in the cells of the wall 

 of the capsule, by the irregular dehiscence of the cap- 

 sule, and (probably) by the development of a true (hypo- 

 basal) foot. 



Section B. Elatereae : the sterile cells in the capsule develope into elaters. 

 a. Thalloid Forms. 



Fam. 2. Metzgeriece : genera, Aneura and Pseudoneura (Riccardia), 



Metzgeria. 



,, 3. Diplomitriftf : Blyttia and Morkia (Pallavicinia), Umbra- 

 culum (Hymenophyton), Pellia, Symphogyna. 

 /3. Foliose Forms. 



Fam. 4. Codoniece : Fossombronia, Androcryphia (Noteroclada), 



Petalophyllum, Blasia. 

 ,, 5. Haplomitriece : Haplomitrium, Calobryum. 



