148 A TEXT-BOOK OF BOTANY 
in other cases the spores are scattered by the wind and the 
infection starts in the tree tops. Almost all full-grown trees 
are diseased at some point. 
86. Puffballs.—The puffballs are fleshy Fungi that differ 
from the mushrooms in having the spores enclosed until 
they are ripe (Fig. 152). 
There is a subterranean 
mycelium, as in the mush- 
rooms; but the  spore- 
bearing structure is a 
fleshy, globular body, con- 
taining irregular cham- 
bers lined with the spore- 
producing layer. When 
young, this body is solid 
and white; but as the 
spores mature, it becomes 
yellowish and brownish, 
gradually dries up, and 
finally is only a brown 
parchment-like shell con- 
taining innumerable, ex- 
Fic. 152.—Puffballs——After Gipson. ceedingly small Spores 
that are discharged by 
the breaking of the shell. Some of the puffballs become 
very large, reaching a diameter of twelve to eighteen 
inches. 
S7. The highest group of Fungi.—The rusts, mushrooms, 
and puffballs represent the highest and most extensive 
group of Fungi, characterized by producing spores by means 
of a basidium, and hence called Basidiomycetes, which means 
“basidium Fungi.’”? The peculiarity of the basidium is 
that it sends out branches, each of which produces a spore 
at its tip (Fig. 147, C). The layers of basidia (spore-pro- 
ducing cells) were noted in the mushrooms and the puff- 
