52 TASMANIAN BRYOPHYTA, 



Marchantiales. — The gametophyte is always a pro- 

 cumbent green thallus. This has in many genera attained a 

 complex structure. In most species an efficient system of 

 air-chambers is formed, communicating with the atmo- 

 sphere through more or less developed pores. The under 

 surface bears scales and copious rhizoids. The organs of 

 reproduction may occur simply on the surface of the frond 

 or may be borne on specially constructed, erect branches. 

 In Riccia, at the one extreme the archegonia are buried 

 in the upper tissue, with their necks just exposed ; in Mar- 

 chantia they grow on a special convex cushion. After 

 fecundation in Riccia the archegonium, with its enclosed 

 sporophyte, sinks into the substance of the frond, and as- 

 sumes the form of a simple spore case. In Marchantia the 

 branch grows erect, the top expanding into an umbrella- 

 like body displacing the fertilised archegonia to the under 

 surface. The sporophytes develop under the protection of 

 this cap, and do not require and do not develop a long 

 stalk. In all except Riccia spiral hygroscopic elators are 

 mixed with the spores. 



JuNGERMANNiALES. — To this Order belong the greater 

 number of Hepatics. The structure of the gametophyte is 

 Yevj varied. In some forms it is a flat green frond of sim- 

 ple outline, bearing the reproductive organs upon the dor- 

 sal or ventral surface or upon short special branches. 

 Others develop marginal expansions, which are considered 

 primitive leaves or lobes of the frond, according to the view 

 taken by the observer, while the greater number of species 

 have true leaves. When this is so these organs are in- 

 serted in three rows, two being lateral and one ventral. 

 The ventral leaves are generally smaller than the others, 

 and are in some species absent. They are generally re- 

 ferred to as underleaves, amphigastria, or stipules. In the 

 region of the archegonia the leaves in most species are 

 much enlarged ; the last ones are often united in a sheath, 

 called the perianth, round the fructification. Sometimes 

 instead of the upper leaves uniting to form the perianth 

 a special development grows up from the stem to form a 

 perianth-like sheath, and is known as a pseucloperianth. 

 The enlarged leaves outside the perianth are called the 

 involucre, or in leafless forms, involucral scales may be 

 formed at the base of the peri an th. The lateral leaves of 

 the involucre are oftrn named bracts, and the correspond- 

 ing underleaf the bracteole. After fertilisation the arche- 

 gonium enlarges round the sporophyte, and forms the 

 calyptra. Some species do not develop a perianth. When 

 this is so the calyptra generally becomes thick and fleshy. 



