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 puffbalh, 

 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, 

 oats, and barley exceeds $25,000,000 

 annually, and that the loss in oats 

 alone exceeds $6,500,000. The 

 damage to corn is probably about 

 equal to that of oats. Some writers 

 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 



FIG. 197. Smut on the oat plant 



Two heads of oats, each with the 

 leaf (0 which sheathes the stalk. 

 The head at the left has matured 

 its grains in a normal manner, 

 while in the one at the right the 

 grains are supplanted by the black- 

 ened masses of the smut. One third 

 natural size 



