156 SECOND GROUP. MUSCINEAE. 



shown in more simple leaves by a more or less deep indentation of the anterior margin, 

 but when the leaves are much divided as in Trichocolea, the two halves which were dis- 

 tinguised in the rudimentary state may still be recognised ; the lower lobe of the leaf is 

 often smaller and differently shaped, turned over and hollowed out. 



In the branching system we can distinguish between the branches which arise on the 

 sides of the stem and beneath the leaves, and those on the ventral side in the axils of 

 the amphigastria, if there are any, or beside them. The lateral branches arise in a 

 large number of the Jungermannieae from the segment in the place of the lower ventral 

 lobe of the upper leaves. Fig. 105 may serve to illustrate this remarkable arrangement. 

 It is a diagrammatic representation of the apical view of a branching shoot ; /, 

 // . . . VI are segments of the apical cell 6* of the main shoot, //and F of the ventral 

 side, /, ///, IV, VI of the dorsal ; the two segments / and /// are each already divided 

 by a longitudinal wall into a dorsal and a ventral half, and the apical cell s of a lateral 

 shoot is already formed in the ventral half by the appearance of the walls i, 2, 3, while 

 each dorsal half of the segments is developing into the half of an upper leaf ; the other 

 segments which do not form shoots become entire two-lobed leaves. This is the 

 process in a great majority of the Jungermannieae, in Frullania, Madotheca, 

 Mastigobryum, Lepidozia, Jungermannia trichophylla, and Trichocolea. In Radula, 

 Lejeunia and some others the basal halves of the segments are not applied to the forma- 

 tion of branches in their entire height and before the appearance of further divisions, 

 but the cells first divide, and a part of the free outer surface of the segment forms the 

 lower leaf-lobes in the normal manner, and shoots spring from the basiscopic portion 

 only. The developed shoots are therefore always inserted at the base of a lateral leaf 

 and close to its lower lobe. 



The branches which grow on the under, the ventral, side of the stem are peculiar in 

 being usually endogenous in origin, proceeding, according to Leitgeb's statements, from 

 mother-cells which lie beneath the layer of cells that forms the surface of the stem. The 

 branches thus formed may appear in acropetal succession or be adventitious, and 

 in some genera, as Mastigobryum and Calypogeia, are the only ones that bear the 

 sexual organs, while in others they develope into whip-like forms, flagella, with leaves 

 that are always small and sometimes only rudimentary. They have the power of 

 remaining dormant for a considerable time, and then bursting forth from older parts of 

 the stem. Jn Lophocolea bidentata the branches are almost entirely formed from the 

 ventral halves of the shoots and endogenously, and so too in Jungermannia bicuspidata, 

 where some branches are exogenous ; in the latter species the branches bend over and 

 so form an apparently pinnate system, and cells of the ventral segments grow out on 

 older specimens into long tubes at the apices of which buds sometimes form. 

 Adventitious shoots are also sometimes formed on leaves. 



b. The Anthoceroteae include the genera Anthoceros, Dendroceros and Notothylas. 

 Anthoceros laevis and punctatus, which grow with us in summer on loamy soil, develope 

 a flat, ribbon-like, leafless thallus, which branches irregularly and forms a circular disk. 

 Dendroceros has a strong mid-rib, from which the flat thallus extends on both sides as 

 a single layer of cells with the margin crisped and folded. In Anthoceros and 

 Notothylas the thallus has more than one layer of cells. The cells of the thallus con- 

 tain only one chlorophyll-corpuscle, and this incloses a spherical amylum-body and 

 conceals the nucleus. Stomata are formed on the under side of the thallus close behind 

 the growing apex, and the intercellular space beneath is filled with mucilage ; here 

 therefore the stomata would be more fitly called mucilage-slits, since their function is to 

 secrete the mucilage which in other tlepaticae is supplied from club-shaped papillae 

 at the apex. The clefts are formed by the splitting of the cell-wall between any two 

 cells of the thallus ; there is therefore no previous special formation of guard-cells, 

 as in Ferns and Phanerogams. Nostoc-colonies are not unfrequently found in the 

 mucilage-cavities, and cause peculiar changes in them ; the organs are attacked by 



