SECOND GR UP. MUSCINEAE. 



time that transitional forms between the two are not wanting. Leitgeb has divided the 

 Jungermannieae into two groups distinguished by the position of the female sexual 

 organs, the acrogynous and the anacrogynous. In the first the growth of the shoot is 

 terminated by the appearance of the archegonia, which are formed in immediate proxi- 

 mity to the apical cell ; in many cases an archegonium 

 is formed from the apical cell itself. To this group 

 belong all leafy forms with radial structure, with the 

 exception of Haplomitrium Hookeri, which differs from 

 it in other respects also. In the second group the 

 archegonia do not rise either on the apex or very near 

 it, but, Haplomitrium only excepted, on the back of 

 the shoot, which usually continues to grow after their 

 formation, though the growth of sexual shoots is some- 

 times cut short, as in Metzgeria^ Aneura, Blasia and 

 some others. 



The sexual organs are distributed monoeciously or 

 dioeciously, and are formed in the thalloid genera on 

 the dorsal surface of the shoot. They are here pro- 

 tected by an envelope, formed either by the curvature 

 of the shoot itself, as in Metzgeria, or by the turning 

 up of the lateral edges of the shoot, or by peculiar outgrowths of the thallus, as in 

 the Haplolaeneae and Diplomitrieae. In the foliose (acrogynous) Jungermannieae 

 the sexual organs are formed on the apex of main shoots or of special small sexual 

 branches which are often on the ventral surface and endogenous in their origin. The 

 antheridia are usually in the axils of the leaves, singly or several together. The 

 archegonia appear, usually in numbers, on the apex of the shoot, either on one which 

 bears antheridia lower down, or on special female branches which are so deeply 



FIG. 102. Sexual organs of Radula com- 

 planata; ar archegonia, an antheridia, b 

 leaf. After Hofmeister. 



A 



FlG. 103. Calypogeia Trichomanis. Longitudinal section of young sexual branches ; iv rhizoids, a archegonia, 

 b leaves of the branches, c wall formed by the branch which has become cup-shaped, st primary stem on which the 

 branch arises. In A the branch is still young ; it has thrust itself obliquely into the ground and has then become curved 

 upwards. After Hofmeister, magn. 200 times. 



excavated in the Geocalyceae, that the archegonia are sunk in a deep pitcher-shaped 

 hollow, a development which is specially striking in Calypogeia (Fig. 103). Where 

 the archegonia are not enclosed in this manner, they have an envelope formed of the 

 adjacent leaves, a perichaetium, and usually a second envelope is found, the 

 perigynium, which lies as a membranous growth round each archegonium. These 

 processes are minutely described by Leitgeb in the case of Radula complanata. 



