348 PART III. THE CLASSIFICATION OF PLANTS. 



several archegonia, the development of them begins in the youngest segment- 

 cells of the growing-point. The archegonia are surrounded by the leaves of the 

 apex ; and in most cases the leaves of the last whorl are coherent, forming 

 an involucre, surrounding the single archegonium or the group of archegonia. 

 In the Jnngerrnannieae Geocalyceae (e.g. Calypogeia, Saccogyna) the invo- 

 lucre arises as an annular outgrowth, forming a large cavity enclosing the 

 archegonia; after fertilisation, it attains a relatively large size, and forces 

 itself partially into the soil (hence the name Geocalyx), which may even root 

 itself. 



The a'chegonia of the thalloid Anacrogynae are borne in median dorsal 

 groups : in the dorsiventral foliose Anacrogynae (Blasia, Fossombronia, Andro- 

 cryphia, Petalophyllum), they are borne singly or in groups on the dorsal 

 surface of the stern, and in the dorsiventral Eielleae singly on the flanks of the 

 stem: in the radial Anacrogynae (Riella helicophylla, Haplomitrium) they are 

 borne singly, scattered over the whole length of the stem as in the former, or 

 confined to the apical region as in the latter. They are in all cases provided 

 with some sort of protective organ. Among the thalloid Anacrogynas the group 

 of archegouia is surrounded, in Metzgeria, Aneura, and Pseudoneura, by an 

 involucre consisting of the short modified gametophore (ventral in Metzgeria) ; 

 in Pellia, Symphogyna, and Sphaerocarpus a group (or each archegonium as 

 generally in Sphaerocarpus) is surrounded by an involucre developed as an out- 

 growth of the tissue of the fertile branch ; in Blyttia, Morkia, Umbraculum 

 (hence termed Diplomitrieae) there is a double involucre, generally resembling 

 the preceding, but the inner involucre (perigynium ?), attains its full develop- 

 ment only after the fertilisation of an archegonium of the group ; finally, in 

 Monoclea, the archegonium becomes overgrown by, and hence sunk in, the 

 tissue of the shoot. Among the foliose Anacrogyn, the archegonia are 

 generally protected by perichsetial leaves, and further by an involucre or 

 perigynium (absent in Haplomitrium) which generally invests a single arche- 

 gonium, and in some cases (Blasia, Fossombronia, Androcryphia) is only 

 developed after fertilisation. In Blasia the growth of tissue subsequently to 

 fertilisation is so active that the fertilised archegonium becomes completely 

 sunk in the tissue of the shoot. 



The autheridia are borne, in all Jungermanniaceae (except Haplomitrium) on 

 the dorsal surface of the shoot ; in Haplomitrium they are borne in three 

 rows on the sides of the apical region. 



In Riella belt copliylla the antheridia are borne sunk in the tissue of the free 

 edge of the membranous wing. As the symmetry of the plant is radial, it 

 presents no distinction of dorsal and ventral surfaces ; still the position of the 

 antheridia in R. helicophylla is dorsal by analogy, since in the dorsiventral R. 

 Reuteri, the wing, which likewise bears the antheridia, is an outgrowth of the 

 dorsal surface of the stem ; antheridia have been observed as yet only in these 

 two species of Riella. 



The antheridia are shortly stalked and are in all cases provided with a pro- 

 tection. In Metzgeria the group of antheridia is invested by an involucre 

 which consists of the short modified ventral gametophore : in the other 

 thalloid Anacrogynae, as also in Androcryphia, Blasia, Petalophyllum, and 

 Kiella, each antheridium is invested by an involucre which grows up around it, so 



