380 
THALLOPHYTES 
or they may have slender branching bodies like the one shown 
in Figure 834. The slender branches may be erect, prostrate, 
Fie. 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- 
or hang in festoons from the 
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 
growing on bark. The asci are produced in 
the small cups. xX }. 
tous 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. 
