ARCHE GONIATE S III 



The fungi are usually Ascomycetes but a few Basidiomycetes also occur 

 as lichens. The fungous filaments wind about the algal cells and usually 

 form a firm superficial protective tissue. The specific characteristics of 

 a lichen depend upon both the alga and the fungus components but the 

 fruiting surface of the lichen is purely fungal. (See page 362.) 



264. BRANCH II. Bryophyta. The Bryophyta include the 

 liverworts and mosses. They are distinguished from the Thal- 

 lophytes by the structure of the gametangia. The sperm cells 

 are provided with two long flagellae and they are formed in large 

 numbers within an oval capsule, the antheridium, whose walls 

 are composed of a single layer of cells. The single egg cell is 

 contained in the lower part of a flask-shaped gametangium, 

 called archegonium. This is also formed by a single layer of 

 cells. The upper portion, or neck, of the archegonium contains 

 an axial row of cells (canal cells) which disintegrate and 

 form a slime through which the spermatozoids make their way 

 to the egg. A " ventral canal cell" cut off from the egg cell 

 at the lower end of the canal cells also distintegrates with the 

 canal cells. 



265. The fertilized egg immediately begins development. 

 There is ultimately formed an organism (sporophyte) which 

 produces spores asexually. From these spores there then 

 develops an organism (gametophyte) which bears the gametan- 

 gia. In this way a regular alternation of sexual and asexual 

 generations occurs. 



266. The Bryophyta are called Archegoniates from the very 

 characteristic female gametangium. They are always holo- 

 phytic and are chlorophyll green. 



267. Class i. Hepaticae. The liverworts are usually thalloid 

 or if there is a differentiation into stem and leaves the latter 

 are arranged dorso-ventrally. The thallus branches dichoto- 

 mously and is attached to the substratum by rhizoids, i. e., tubu- 

 lar, hair-like cells which serve as organs for the absorption of 

 moisture. The spore capsules usually contain sterile elongated 



