850 PART III. THE CLASSIFICATION OF PLANTS. 



Though the mode of growth of the epibasal half of the embryo is most com- 

 monly that described above, it not infrequently happens that the growth of the 

 two longitudinal halves is unequal, owing to the fact that the first longitudinal 

 wall is not perpendicular to the basal wall, but is oblique. Consequently the 

 apex is occupied by the two cells of the longer half, and in those cases in which 

 the apical growth is long-continued the result is that the capsule may be de- 

 veloped entirely from one longitudinal half of the embryo. This mode of 

 development has been observed in Blasia, Pellia, Fossombronia, Haplomitrium, 

 and Symphogyna ; in Fossombronia and Symphogyna an embryo of this 

 kind appears to grow in length, for a time at least, by means of a two-sided 

 apical cell. 



In many of the Jungermanniacea? (e.g. Pellia, Lepidozia, Jungermannia, 

 Calypogeia, Frullania) the lower end of the seta developes into a bulbous mass 

 of cells forming a false foot, the upper margin of which grows up so as to form 

 a sheath round the lower part of the seta in some cases. 



The development of the hypobasal portion of the embryo is comparatively 

 insignificant; in most cases it is merely a small appendage to the lower end of 

 the seta. The hypobasal cell enlarges somewhat, without undergoing any 

 division (e.g. Radula, Madotheca, Lepidozia, often in Pellia and Symphogyna) ; 

 or it undergoes transverse division to form a filament of two or three cells, the 

 lowest of which becomes elongated and grows down among the cells at the base 

 of the archegonium (e.g. Metzgeria, Aneura, Jungermannia bicuspidata) ; or it 

 divides by a longitudinal wall into two cells which gr >w out into papillae 

 (Frullania dilatata), or, by further division its produces four papillae (Calypogeia 

 TrMtonumit) ; or, finally, it divides irregularly to form a small group of cells 

 (Blasia). In some forms, however (e.g. Fossombronia, Petalophyllum, probably 

 also Sphasrocarpus, Riella helicophyila, Notarisii, and Eeuteri), the hypobasal 

 cell appears to give rise to a true foot, bulbous in form, comparable to that of 

 the Marchantieae (see p. 340). 



In the further differentiation of the capsule, the cells of the amphithecium 

 undergo periclinal division so that the wall eventually consists of two or more 

 (up to six) layers of cells ; though in Haplomitrium, Sphaerocarpus, and Riella, 

 the wall consists throughout of a single layer of cells. In the wall-cells annular 

 thickenings are developed, which are usually transverse ; but in Haplomitrium 

 there is a single annular thickening situated longitudinally ; the cells are un- 

 thickened in Spheerocarpus and Riella. The planes of dehiscence of the cap- 

 sule, except in those forms which dehisce irregularly (Riella, Sphasrocarpus), are 

 marked out by four longitudinal rows of small-celled tissue which correspond 

 in position with the walls between the four apical cells of the growing embryo. 



The archesporium, which is co-extensive with the endothecium, presents 

 various degrees and forms of differentiation. In Riella and Sphasrocarpus it 

 comes to consist of a number of cubical cells, some of which become the 

 mother-cells of the spores, whereas the others persist as unaltered sterile cells. 

 In all the other Jungermanniaceae some of the cells of the endothecium are 

 sterile, but they develope into elaters, becoming elongated in form and spirally 

 thickened, having sometimes two spirals (Haplomitrium, Plagiochila, Scapania, 

 Jungermannia, Lophocolea, Lepidozia, Eadula, Fossombronia, Symphogyna, 

 Blasia, etc.), or only one (in the Jubuleae, e.g. Lejeuuia, Frullania, and in 



