430 



BOTANY 



niaceae, however, show a distinct segmentation into stem and leaflets. The 

 latter consist of one layer of cells without a midrib, and are inserted with ob- 

 liquely directed laminse in two rows on each flank of the stem. Some species 

 (e.g. Frullania Tamarisci, a delicately branched Liverwort of a brownish colour 

 occurring on rocks and tree-trunks) have also a ventral row of small scale-like 

 leaves or amphigastria (Fig. 386 a). The dorsal leaves are frequently divided into an 

 upper and lower lobe. In species growing in dry places, like Frullania ?'///"//*</, 

 the lower lobe is modified into a sac, and serves as a capillary water-reservoir. The 

 leaves regularly overlap each other ; they are then said to be succubous, when the 

 posterior edges of the leaves are overlapped by the anterior edges of those next 

 below (Frullania, Fig. 386), or in- 

 cubous, if the posterior edges of the 

 leaves overlap the anterior edge* of 

 the leaves next below (Plagwchilii, 

 Fig. 385). 



The branching stems of the foliose 



'ws 



FIG. 380. Part of a shoot of Frullaiiia 

 Tamarisci, seen from below. >, Dorsal 

 leaves with the lower lobes (u) modified 

 as water-sacs ; <i, amphiKastriiuii. ( x 

 36.) 



FIG. 387. Haplormitrium Hookeri. a, origin of 

 a new shoot r, rhizome ; o, lower limit-of 

 tin- iii-rial shoot. (After OOTTISCHE.) 



Jungermamiiaceae are either prostrate or partially erect, and in consequence of the 

 manner in which the leaves develop, present a distinctly dorsiventral appearance. 



The long-stalked sporogonium is also characteristic of this order ; it is already 

 fully developed before it is pushed through the apex of the archegonial wall by 

 the elongating stalk. It has a spherical capsule which on rupturing splits into 

 four valves (Figs. 384, 385). No columella is formed in the capsule ; but in 

 addition to spores it always produces elaters, which, by their movements while 

 drying, scatter the spores. The stalk of the capsule is delicate. The wall of the 

 capsule (usually two or several cells thick) consists of cells with annular or band- 

 like thickenings, or the walls are uniformly thickened with the exception of the 

 outermost walls. Dehiscence is dependent on the cohesive power of the water in 

 these cells causing the outer walls to bulge into the cavity. 



According to the position of the sexual organs and sporogonium the Junger- 

 manniaceae are divided into two groups. In the Anakrogynae the apex is nut 

 used up in the formation of the archegonia, and the sporogonia are situated on 



