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which attack corn crops, the whole class of which grow 
upon some kind of organized matter, and none of them 
derive their nourishment directly from the soil or atmos- 
phere, like other plants. It is doubtful whether they will 
grow on plants perfectly healthy, or if they do not always 
attack some part where disease or decay had already effected 
some alteration in the tissue. These fungi are exceedingly 
small, and the seeds of them (their sporules) smaller than the 
dust of the puff ball. The sporules of the Puccinia graminis, 
or mildew, are minute club-shaped bodies, which enter the 
plant through the pores (stomata,) and vegetate below the 
epidermis of the plant, which in their growth they raise 
and blister, and when arrived at maturity burst through it, 
and then form spots or irregular blotches of various colours. 
The Puccinia graminis attacks only wheat and barley ; it 
makes its appearance on the upper leaf, and then on the 
lower leaves and stem, in the forms of white spots, similar to 
spots made by rain on new cloth. In a close moist (muggy) 
season it vegetates most rapidly ; for in such weather the 
plants remain longer succulent, their pores expanded and 
their fibres relaxed. In a dry season the mildew is seldom 
seen. The crops on clayey soils are seldom attacked except 
in small patches, and it seems to infest crops growing on par- 
ticular soils, and that in the following order. 
1. Wheat growing on dunghills always attacked. 
2. Peat, or moor soils. 
3. Calcareous. 
4. Calcareous loams. 
5. Sandy soils. 
6. Sandy loams. 
7. Clays. 
White wheat is always the earliest affected, and the 
bearded the last. The fungus is communicated from the soil 
to the crop. Its seeding time is from May to October. In 
the soil on which the seeds alight, they attach themselves, 
