324 



PART IV. CLASSIFICATION. 



are ripe. In the Riccieae the spores are set free by the gradual disorgan- 

 isation of the calyptra and of the tissue of the thallus in which the 

 cah-ptra is embedded ; in the other Marchantiacese the capsule is forced 

 out of the catyptra by the elongation of the short stalk. 



The order Marchantiacese includes the families Kicciese (Riccia, Oxy- 

 mitraX Corsinieae (Corsinia, Boschia), and Marchantiese (Marchantia, 

 Lunularia, Fegatella, etc.). 



Order II. Jungermanniaceae. 



A. The GAMETOFHTTE. On germination the spore gives rise to a proto- 

 nema which may be a solid ellipsoidal mass of cells (as in Pellia) with a 

 root-hair at one end ; or a flattened plate of cells (Eadula, Frullania) ; or 



a filament, some- 



f " times branched 



(Lophocolea, 

 C h i 1 oscy phus) ; 

 however, the 

 differences in 

 form of the 

 protonema are 

 not of great 

 morphological 

 importance 

 since, in many 

 cases, flattened 

 and filamentous 

 forms have been 

 found to be pro- 

 duced from 

 spores of the 

 same plant. 



The protone- 

 ma gives rise to 

 the adult shoot 

 by the forma- 

 tion, either from 

 a marginal cell, 

 if it is flat, or 



from the terminal cell, if it is filamentous, of a growing-point with a 

 s ingle apical cell. 



The Morphology of the Adult Shoot. The adult shoot may be differenti- 

 ated into stem and leaf, as in ihefoliose forms ; or undifferentiated, as in 

 the thalloid forms. Its symmetry is generally dorsiventral ; the only 

 radially symmetrical, erect-growing forms being Haplomitrium and some 

 species of Riella (e.g. R. hellcophijlla and Parian). 



Most of the thalloid forms have a distinct midrib. The shoot bears 

 numerous unicellular root-hairs, as also club-shaped glandular hairs 

 which secrete mucilage, on its ventral (under) surface. In the dorsi- 

 ventral foliose forms, the stem bears a row of leaves on each flank, and 



FIG. 200. Growing-point of thallus of Metzgeria furcata : t apical 

 cell ; sf etc., successive segments ; m' m" marginal cells ; p' super- 

 ficial cell ; i t cells of the midrib ; c clavate hairs. ( x 540 : after 

 Strasburger.) 



