252 INTRODUCTION TO BOTANY 
members of the grass family ; another sub-division is the rusts, 
found wherever wheat and oats are grown, and also appear- 
ing upon many other host plants; mushrooms and puffballs, 
another sub-division, are widely distributed wherever there is 
a good supply of decaying organic matter, and some grow as 
parasites upon living trees. Because of the 
frequency of the parasitic habit in the stalk 
fungi, it is evident that the group is one of 
great importance to industries that depend 
upon the growth of plants. 
239. Damage from smuts. The 
cereals are particularly affected by 
these parasites, since all of the 
smuts are parasitic and since the 
grains seem to be especially fav- 
orable hosts for them. Different 
writers present very different esti- 
mates of the amount of damage 
done to our crops annually by 
these parasites, but a conservative 
estimate made by the United States 
Department of Agriculture states 
that the loss from smut in wheat, 
Two heads of oats, each with the 
leaf (1) which sheathes the stalk. oats, and barley exceeds $25,000,000 
The head at the left has matured annually, and that the loss in oats 
its grains in a normal manner 
while in the one at the right the alone exceeds $6,500,000. The 
grains are supplanted by the black- damage to corn 1s probably about 
ened masHesofthesmint. Oneshind sayal to that of dats. Some writers 
natural size 
estimate the loss to our crops as 
several times greater than the above conservative estimates. 
Whatever may be the exact loss, it is evident that the matter 
is one of great significance. 
240. Corn smut. This smut (Ustilago maydis) is ordinarily 
first noticed when it forms whitish masses in the ear or tassel 
or upon other parts of the corn plant. These masses develop 
into spores and become black, sticky, and unsightly. But 
Fre. 197. Smut on the oat plant 
