74 MOSSES AND FERNS CHAP. 



ing spores. The sporogonium remains within the calyptra 

 until the spores are ripe, when by a rapid elongation of the cells 

 of the seta it breaks through the calyptra, which is left at its 

 base, and the capsule then opens. The opening of the capsule 

 is usually effected by its walls splitting into four valves along 

 lines coincident with the first formed vertical cell walls in the 

 young embryo. These valves, as well as the elaters, are 

 strongly hygroscopic, and by their movements help to scatter 

 the ripe spores. The latter show much the same differences 

 observed in the Marchantiaceae. When the spores germinate 

 at once they have abundant chlorophyll and a thin exospore, but 

 where they are exposed to drying up, they have no chlorophyll 

 and the exospore is thick and usually with characteristic thick- 

 enings upon it. From the germinating spore the young 

 gametophyte may develop directly, or there may be a well- 

 marked protonemal stage. This latter is always found in the 

 foliose forms, and is either a flat thallus, like the permanent 

 condition of the lower thallose genera, or sometimes (Proto- 

 cephalozia) it is a branched filamentous protonema, very much 

 like that of the Mosses, and sometimes long-lived and produc- 

 ing numerous gametophores. 



Non-sexual reproductive bodies in the form of unicellular 

 gemmae are found in many species, and in Blasia special 

 receptacles with multicellular gemmae something like those of 

 Marchantia occur. 



The Jungermanniales naturally fall into two well-marked 

 series, 1 Anacrogynae and Acrogynae, based upon the position 

 of the archegonia. These in the former are never produced 

 directly from the apical cell of a branch, in the latter group 

 the apical cell of the archegonial branch always sooner or later 

 becomes transformed into an archegonium. The Haplomitrieae 

 show some interesting intermediate forms between the two 

 groups, but all the other Jungermanniales examined belong 

 decidedly to one or the other. As a rule the Anacrogynae are 

 thallose (the "frondose" forms of the older botanists), but a 

 few genera, especially Fossombronia, show a genuine formation 

 of leaves. All the Acrogynae have a distinct slender stem with 

 large and perfectly developed leaves. 



1 Prof. L. M. Underwood proposes the name Metzgeriaceae for the Ana- 

 crogynae, reserving the name Jungermanniaceae for the Acrogynae. These 

 two groups he considers co-ordinate with the Marchantiales and Antho- 

 cerotes. 



