104 MANUAL OF BOTANY 



Class IV.— HEPATIC^ (LIVEBWOBTS). 



The differences which are met with between this group and 

 the succeeding one chiefly concern the sporophyte. In the 

 Hepatioae the sporogonium is never set free from the calyptra 

 tni the spores are mature ; the calyptra is never carried up as a 

 cap to the sporogonium, but the whole of it remains as a 

 vagiuula ; there is no gradual elongation of the seta. Except m 

 the Anthocerotacese there is no columella in the sporogonium, 

 but the whole of the endothecium becomes the archesporium ; 

 except in the Biccie» sterile cells, generally elaters, are developed 

 as well as spores from the archesporial tissue. The vegetative 

 body is less differentiated anatomically than in the Mosses ; 

 there is never any vascular tissue indicated in either sporophyte 

 or gametophyte, nor are stomata present in the epidermis of the 

 former, except in Anthoceros. 



There are two types of structure found in the group, in one 

 of which the gametophyte is a thallus or thaUoid shoot, in the 

 other it is a leafy shoot. These are spoken of as thallose and 

 foliose respectively. The former include the two orders 

 Marohantiaceae and Anthocerotaceae, the latter are fomid among 

 the Jungermanniaceae. 



Thallose Liverwoets. — A typical representative of the 

 thallose liverworts is Marchantia polymorpha, the structure of 

 which may be described in detail. From the spore there is 

 developed a small protonema, which, at first filamentous, expands 

 into a flat cellular plate, on which arises by budding the body of 

 the plant. This has a thick creeping dichotomously branching 

 thalloid stem, from the under side of which a number of root hau"s 

 or rhizoids are given off. It also bears on the lower surface two 

 rows of scaly leaves. The upper surface is somewhat corrugated 

 and bears the sexual organs on special receptacles or gameto- 

 phores ; it also gives rise to a number of circular gemmae cups or 

 cupules, in which the gemmae arise from superficial cells (Jig. 866). 



The shoot is dorsiventral, the two surfaces showing marked 

 differences in structure. 



The upper surface is marked by somewhat indistinct lines, 

 dividingit into a mnnber of lozenge-shaped or rhomboidalareas, in 

 the centre of each of which is a peculiar opening or pit leading 

 into an air-chamber, which is bounded above by a single layer 



