342 



PART IV. VEGETABLE TAXONOMY. 



reproduced vegetatively, also occur in abundance on the upper 

 surface of the branches. One of these, and one of the gemmae 

 magnified, are shown in Fig. 550, g and m. 



(D) The Jungermanniacese constitutes the largest order 

 of the Hepaticse. A few of them have thalloid, but the great 

 majority, foliose stems. They produce solitary capsules which 

 ordinarily split into four valves, from the apex downwards, and 

 produce numerous spores and spiral elaters. 



Among the leafless forms are Blytia, Pellia, Aneura, Blasia, 

 and Metzgeria. Metzgeria furcata has a dichotomously- 

 branched, narrow thallus composed 

 of a single stratum of cells, except 

 the midrib, which, includes several 

 layers. It is not uncommon on tree 

 trunks in damp woods. In most of 

 the thalloid forms, the archegonia 

 are produced on the upper surface 

 and not at the apex of the thallus. 



In the foliose forms the leaves 

 occur, as has already been described, 

 in three longitudinal rows, and two 

 of the rows are conspicuous and 

 spread out laterally, while the third 

 occurs on the shaded or under side, 

 and its members are not so well de- 

 veloped. The fruits occur singly on 

 stalks at the ends of the branches. 

 See Fig. 551. Many of the species are common in damp soil 

 and on tree trunks. They are plants of wide distribution, occur- 

 ring both in the northern and southern hemispheres. Junger- 

 mannia, Calypogeia, Geocalyx, Gymnomitrium and Plenranthe are 

 among the genera. 



Class II.— The Musci (Mosses). 

 The Musci or Mosses are all leafy-stemmed plants, and the 

 leaves are all of the same kind and very seldom two-ranked. 

 The spores produce a confervoid protonema which may increase 

 indefinitely by an apical growth, but sooner or later gives rise to 

 lateral buds which develop into the leafy plant. See Fig. 548. 

 When the germ-cell develops in the archegonium, the latter 



Fig. 551 — Jungermannia bidentata. 

 s, sporogonium dehiscent into four 

 valves. 



