GROUP II. BRYOPHYTA : HEPATKLE. 349 



that it appears to be sunk in the tissue of the shoot. In Fossombronia, Haplo- 

 mitrium, and the Acrogynae, the antheridia are protected by the leaves : in the 

 Acrogynaa the antheridia are borne, singly or several together, in the axils of 

 leaves ; and in some forms (e.g. Scapania, Lejeuuia, Frullania) the upper lobe 

 of the protecting leaf is modified in form. 



The distribution of the sexual organs varies even in the species of some of the 

 genera. Among the Anacrogynae, Metzgeria, Pseudoneura, Morkia, Umbra- 

 culum, Petalophyllum, Spliaerocarpus, Haplomitrium, Blyttia (generally), and 

 Stella helicophylla, are dioecious; whereas Pellia, Aneura (some species), 

 Fossombronia, Symphogyna, Androcryphia, and Itiella Reuteri, are generally 

 monoecious. In the monoecious forms the antheridia and archegonia ate 

 generally borne on distinct branches (diclinous), but sometimes on the pame 

 branch (monoclinous), as in Androcryphia and occasionally in Blyttia. When 

 a dorsiventral shoot bears only antheridia or archegonia, they are developed in 

 the median line ; but when it bears both organs, the archegonia are median and 

 the antheridia lateral. 



The Acrogynaa are generally monoecious and diclinous. 



The structure of the adult shoot of the Jungermanniaceaa is very simple. In 

 thalloid forms which have no midrib, the shoot consists of parenchymatous 

 cells forming a single layer at the margin and several layers (e.g. Pellia, 

 Aneura, Sphaerocarpus), in the middle line of the shoot ; in those which have a 

 midrib (e.g. M>tzgeria, Symphogyna, Blyttia, etc.), the midrib consists of 

 several layers of cells, whereas the lamina consists of only a single layer. In 

 Symphogyna and Blyttia the midrib is traversed by a strand of elongated 

 prosenchymatous cells having thickened and more or less pitted walls. In 

 Blasia the stem has an axial strand of elongated cells with delicately pitted walls. 



In the Acrogynaa, the stem generally consists of an axial strand of relatively 

 thin-walled cells, surrounded by a cortex of narrow thick-walled cells; but in 

 those forms which give rise to endogenous ventral branches (e.g. Calypogeia) 

 the cortical cells of the ventral surface of the stem are not thick-walled. The 

 leaves are simply single layers of similar cells, and have no midrib. 



The root-hairs are, in all cases, destitute of the peculiar thickenings so 

 characteristic of the Marchantiaceae. 



B. The SPOKOPHITE. The course of the development of the sporophyte is, 

 in its main features, essentially the same throughout the Jungermanniaceae. 



The oospore is divided by a transverse (basal) wall into two halves, epibasal 

 and hypobasal. The epibasal cell gives rise to the capsule and its stalk (seta). 

 It divides transversely, and the longitudinal divisions follow in both cells so 

 that the epibasal half of the embryo consists of two tiers of each consisting of 

 four cells. Further growth in length is effected by the cutting off, by trans- 

 verse walls, of segments from the cells forming the apical tier ; but this apicnl 

 growth is arrested, sooner or later, by the formation of walls parallel to the free 

 surface (periclinal) in the apical cells, and also frequently in some of those 

 below them, which indicate the differentiation of the capsule-wall (amphi- 

 thecium) from the intprnal mass of cells (endothecium) which give rise to the 

 spores and elaters. The cells below the capsule may, however, continue to 

 grow and divide transversely, and by means of this intercalary growth the full 

 length of the seta is attained. 



