192 



I. ANACROGYN^;. The archegonia are situated on the upper 

 side of the thallus or stem, placed laterally., and covered by an 

 " involucre," formed by the calyptra together with the tissue of 

 the stem or thallus. 



a. ANELATEREJ:. Without any elaters : Sphcerocarpus, Hiella. 



b. ELATEREJ:. a. Thalloid : Aneura pinguis, in damp situations ; 

 Metzgeria furcata, on trees ; Pellia epiphylla, in damp situations ; 

 Blasia pusilla, on damp clay soil, in the shade (scales are present 

 on the thallus) . ft. Foliose and ot dorsiventral : Haplomitrium 

 hookeri. 



II. ACROGYNJ:. The apex of the stem or of certain branches is 

 adapted for the formation of female shoots. The archegonia are 

 most frequently aggregated on the apex of the shoots, and are 

 encircled by their leaves (perichaetium). Between these and the 

 archegonia, enclosing the latter, a peculiar cup-shaped organ (the 

 involucre) is formed. This group only includes leaf-bearing 

 genera : Frullania, Radula, Madotheca, Ptilidium, Calypogeia, 

 Lepidozia, Mastigobryum, Lophocolea, Jungermannia, Scapania, 

 Plagiochila. 



Class 2. Musci frondosi or .veri (True Mosses). 



In this class the protonema is well developed, and resembles a 

 branched filamentous Alga, from which it can be easily distin- 

 guished by its oblique septa (in Sphagnum it is a cellular expan- 

 sion). The Moss-plant, which is developed directly from the 

 protonema, generally has an erect, thick, cylindrical stem similarly 

 constructed on all sides. The leaves are arranged spirally, the 

 most frequent divergence being |- or ^ (Fig. 200 -4). A midrib is 

 often present and also marginal veins formed by longitudinally 

 elongated cells ; at these veins the leaf is more than one layer in 

 thickness. In Leucobryum the leaves are generally constructed 

 of more than one layer. 



The stem grows by means of a three-sided, pyramidal, apical cell 

 which gives rise to three rows of segments, each segment forming 

 a leaf. The lateral branches arise from the lower portions of the 

 segments, the upper portion of which does not take any part in the 

 construction of the leaf. From their mode of origin the branches 

 are not axillary, and differ in this respect from the Flowering- 

 plants. 



The ventral portion of the archegonium is very early ruptured 



