odO PART IV. CLASSIFICATION. 



Section B. Elatereae : the sterile cells in the capsule develope into 



elaters. 



o. Thalloid Forms : Metzgeria, Aneura, Pellia, etc. 

 ft. Foliose Forms : Fossombronia, Blasia, Haplomitrium (with radial 



symmetry), etc. 

 Series II. ACBOGYN^: : growth in length arrested by the development of 



archegonia ; all foliose. 



This series includes a number of families of which the more 

 familiar genera are Plagiochila, Jungermannia, Scapania, 

 Lepidozia, Badula, Lejeunia, Frullania; etc. 

 Order III. Anthocerotaceae. 



A. The GAMETOPHYTE. The protonema developed from the germinating 

 spore is a flattened plate of cells ; in Anthoceros the formation of the 

 flattened plate is sometimes preceded by the outgrowth of the contents 

 of the spore, covered by the endospore. into a filament at the apex of 

 which the plate of cells is developed. The adult shoot is developed as a 

 lateral out-growth from the flattened protonema. 



The Morphology of the adult shoot. The adult shoot is thalloid, and its 

 symmetry is dorsiventral. It is semi-circular, or nearly circular, in out- 

 line in Anthoceros. There are no ventral scales 

 on the under surface, but numerous unicellular 

 root-hairs. 



The growth of the shoot is effected, in Antho- 

 ceros, by a series of marginal growing-points. 

 In the growing-point there is a row of initial 

 cells, each of which acts as an apical cell ; their 

 form is wedge-shaped in Anthoceros, dorsal and 

 ventral segments being alternately cut off by 

 the formation of oblique walls. 



(nat size) K the *ca "sules* Branching, or at least the formation of new 



some as yet unopened. growing- points, takes place in the manner de- 



scribed for the Marchantiacese (p. 132). 



The sexual organs are developed from the dorsal segments formed in the 

 growing-point, and are situated in the middle line behind each growing- 

 point in Anthoceros. The antheridia are developed endogenously, and 

 remain enclosed in the tissue until maturity ; they are developed either 

 singly (some species of Anthoceros) or in groups. The archegonia are 

 sunk in the tissue, the apex of the neck reaching to the dorsal surface of 

 the shoot. The shoots are monoecious ; the sexual organs are sometimes 

 intermingled in the same group (frequently in Anthoceros). 



The structure of the adult shoot. The adult shoot of Anthoceros consists 

 of several laj r ers of cells in the middle line, thinning out to a single layer 

 of cells at the margins. The tissue in the middle line consists of longi- 

 tudinally elongated cells, the walls of which, especially in the older parts 

 of the shoot, frequently present reticulate or even spiral thickening. 



The chloroplastids of the Anthocerotaceae are peculiar, on account of 

 their relatively large size, and of the fact that they occur singly in the 

 cells and contain a pyrenoid (see p. 71). 



