306 FIRST FORMS OF VEGETATION. 
alternate stalk presenting this amorphous appear- 
ance. When one of the heads thus affected is 
Fic. 44.—USTILAGO CARBO. 
pulled and examined, 
every chaffy scale is 
found to be filled 
with a firm black 
matter, like soot ag- 
glutinated by mois- 
ture. This strange 
phenomenon is attri- 
buted to the state of 
the air, to the condi- 
tion of the seed, or to 
the character of the 
soil; but there are 
few comparatively 
who are aware of its 
vegetable origin——who know that it is owing to 
the development of minute parasitic fungi, favoured 
of course by unhealthy condi- 
y) 4 soil. 
Fic. 45.—TILLetTia 
tions of the atmosphere and the 
To botanists it is known 
under the name of Ustdlago carbo 
(Fig. 44),and by farmers it is fami- 
liarly called smut or dust-brand. 
It is more frequent in corn than 
CARIES. in any other of the cereal crops. 
Spores and Mycelium 
highly magnified. | Examined under the microscope 
