380 



THALLOPHYTES 



or they may have slender branching bodies Kke the one shown 

 in Figure 334- The slender branches may be erect, prostrate, 

 ^^^ or hang in festoons from the 

 ?) 1^1^ branches of trees or other sup- 

 ports. 



A Lichen, although regarded 

 as a plant, is a structure formed 

 by the association of a Fungus 

 and an Alga. The Fungus in- 

 volved is in nearly all cases an As- 

 comycete, and the Alga involved 

 is nearly always a unicellular 

 form of the Green Algae or some 

 form of the Blue-green Algae. 

 The Fungus is a parasite on the 

 Alga, obtaining food from the 

 Alga. The hyphae of the Fungus 

 get food from the Alga by being 

 in close contact, and since the 

 cells of the Alga are rarely pene- 

 trated, the Alga apparently is not 

 A section through a Lichen, as shown in 



Fig. 332. — Lichens on an Apple 

 branch. From Bulletin 185, Maine 

 Agr. Exp. Sta. 



injured in most cases. 

 Figure 335, shows a 

 meshwork of hyphae 

 and in the meshes the 

 cells of the Alga are 

 held. Usually the hy- 

 phae are more closely 

 interwoven in the outer 

 region, thus forming a 

 compact cortical region 

 which encloses the 

 looser region within 

 where the cells of the 

 Alga are usually more 

 abundant. On the 

 under surface filamen- 



FiG. 333. — A Lichen with a flat lobed body 

 growing on bark. The asci are produced in 

 the small cups. X h- 



tons structures are developed which attach the plant body to the 

 substratum. The mycelium of the Fungus thus constitutes the 

 framework of the plant body or thallus. 



