44 A LABORATORY MANUAL OF BOTANY 
upon stones and bark? Make sketches illustrating some of 
the forms. 
Color.—Note the color. Is it uniform in all specimens 
present? Does the color change when specimens become 
wet? Compare the color with that of leaves and the molds. 
Structure.—Place a small piece of lichen upon a slide 
and dissect as completely as you can. Mount and examine. 
Note the two elements which compose the lichen; the almost 
colorless filamentous part is a plant belonging to the fungi, 
the group of plants to which the molds belong; the green 
part is usually made up of unicellular organisms belonging 
to the alge, or seaweed group of plants. These two plants 
live together in a combination called the lichen. This is 
not one plant, but a combination of plants of two kinds, that 
live together in a very intimate relationship. Each plant 
reproduces itself—the alga by having its body divide into 
two new cells and the fungus by forming spores. Conse- 
quently the lichen as such does not reproduce itself directly, 
although the plants that compose it may reproduce them- 
selves and eventually form new lichens. On lichen bodies 
at certain times there will be seen cup-like outgrowths. It 
is in these that the fungus elements of the lichen form 
spores. These spores may be seen in the ends of some of 
the filaments by carefully dissecting a part of the cup and 
examining it under magnification. 
What advantage does the fungus obtain by having the 
alga grow with it in this way? 
What advantage does the alga obtain? For example, does 
it get food material it could not otherwise obtain? Is it less 
likely to suffer from drying? Does the position of the alga 
in the lichen body indicate that it is protected bythe fungus? 
Does this position favor the use of the alga by the fungus? 
Does this combination assist the alga to grow in places 
where alone it would not grow? Can the lichen grow in 
places where neither element could grow alone? 
