52 BOTANY AND PHARMACOGNOSY. 



Vegetative propagation may ensue by the lower portion 

 of a branch dying and the upper portion continuing as an inde- 

 pendent plant. Or special shoots known as gemmae, may arise 

 either on the margin of the thallus or in peculiar cupules, which 

 when detached by rain or other means, are capable of growing and 

 producing a new plant. 



In addition the thallus body produces both antheridia and arch- 

 egonia (Fig. 29) which may rise on special stalks above the sur- 

 face. After fertilization of the egg-cell which completes the work 

 of the sexual generation or gametophyte, the sporophyte develops 

 producing a sporogonium consisting of a short stalk which is 

 embedded in the tissues of the gametophyte, and a capsule (spor- 

 angium). The latter at maturity dehisces or splits and sets free 

 the spores, which are assisted in their ejection by spirally banded 

 cells called " elaters " (Fig. 31, C-F). The spores on germination 

 give rise to a protonema which then develops a thallus bearing the 

 sexual organs. As in the mosses the sporogonium represents the 

 asexual generation known as the sporophyte. 



Liverwort Groups. -There are three important groups of 

 Liverworts: (i) The marchantia group (Fig. 29) in which 

 the thallus is differentiated into several layers and so somewhat 

 thickened. Another character is the diversity in form of the 

 sexual organs which range from those which are quite simple to 

 those which are highly differentiated. In Riccia the sexual organs 

 are embedded on the dorsal (upper) side of the thallus, while in 

 Marchantia they are borne upon special shoots, one, which has a 

 disk at the apex that bears the antheridia, known as the antheridio- 

 phore, and one, the apex of which consists of a number of 

 radiate divisions and bears the archegonia (Fig. 29) on the lower 

 surface, known as the archegoniophore ; these being borne on sep- 

 arate plants. In Riccia, the simplest of the Liverworts, the spor- 

 angium is enclosed by the thallus and the spores are not liberated 

 until the decay of the plant. 



(2) The JuNGERMANNiA Group, known as " Leafy Liver- 

 worts " or " scale mosses," includes those forms which are more 

 or less moss-like and develop stems and small leaves. The sporo- 

 gonium has a long stalk and the capsule is 4-valved, i.e., separates 

 into four longitudinal sections at maturity. 



