vir] Smuts 83 
in their turn give rise to tertiary spores from which an 
infection tube is produced. It is sufficient for our 
purpose to know that the spores adhering to the wheat 
grain germinate and eventually infect the young wheat 
plant. They are said to retain their capacity for 
germination for seven or eight years. When the young 
plant is infected the mycelium grows as in the case of 
os 
Fig. 26. Spores of Qilletia caries as seen under a microscope. 
Ustilago, without killing the cells of the host, and the 
spores are formed within the mycelium. Usually all the 
grains of the attacked plants are filled with spores. The 
damage done by this pest is not only the loss of yield due 
to the damaged grain for this is only small in proportion 
to the total, but on grinding wheat which is infected the 
flour has a dirty appearance and the peculiar odour of 
6—2 
