t.=--This disease and the one following resemble the
bacterial wilt so closely, as far as external characters go, that they
are difficult to tell apart. The parasites, however, differ so
materially in their nature and life history that the field treatment is
quite different. There are also differences in geographical distribution
that are important, for while the Fusarium wilt occurs occasionally
throughout the southern states, it is known to be of general commercial
importance only in southern Florida and southern California.

_The symptoms of the disease_ are a gradual wilting and dying of the
plants, usually in the later stages of their development. Young plants
die, however, when the soil infection is severe. There is a browning of
the woody portions of the stem, and when a section of this is examined
under a compound microscope the vessels are found to be filled with
fungous threads, which shut off the water supply.

_The infection_ in the Fusarium wilt appears to come entirely from the
soil. Little is known of its manner of spread, except that the
cultivation of a tomato crop in certain districts appears to leave the
soil infected so that a crop planted the next year will be injured or
destroyed. The fungus does not remain in the soil for a very long time
in sufficient abundance to cause serious harm. A rotation of crops that
will bring tomatoes on the land once in three years has been found in
Florida to prevent loss from Fusarium wilt.

_This fungus does not attack any other crop_ than tomatoes, so far as
known, though it is very closely related to species of Fusarium
producing similar diseases in cotton, melon, cowpea, flax, etc. Fusarium
wilt has not been found in fields and gardens in the northern states,
but tomatoes in greenhouses there are sometimes attacked by it or a
related Fusarium, which also occurs in England. When greenhouse beds are
infected the soil for the next crop should be thoroughly sterilized by
steam under pressure.

=Sclerotium wilt.=--This disease resembles the two preceding in its
effect on the plant, which wilts at the tip first, and gradually dies.
Its geographical range is more restricted. It seems to be confined to
northern Florida and the southern part of Georgia and Alabama, where it
occurs in gardens and old cultivated fields. The fungus causing this
wilt attacks the root and the stem near the ground, working in from the
outside. There is not the browning of the wood vessels ch