aracteristic of
the two preceding diseases. If an affected stem is put in a moist
chamber made from a covered or inverted dish, there will develop an
exceedingly vigorous growth of snow-white fungous mycelium which, after
a few days, bears numerous round shot-like bodies, at first
light-colored, then becoming smaller and dark-brown. These are the
sclerotia or resting bodies of the fungus. This fungus, called
_Sclerotium_ sp., or "Rolf's Sclerotium," is noteworthy because it
attacks potatoes, squash, cowpea, and a long list of other garden
vegetables and ornamental plants. The only satisfactory means of control
is rotation of crops, using corn, small grain, and the Iron cowpea, a
variety immune to this and other diseases. Susceptible crops should be
kept from infected fields for two or three years.

=Root-knot= (_Heterodera radicicola_ (Greef) Muel.) attacks tomatoes in
greenhouses and is in some cases an important factor in southern field
culture. It is caused by a parasitic eelworm or nematode, of minute
size, which penetrates the roots and induces the formation of numerous
irregular swellings or galls, in which are bred great numbers of young
worms. The effect on the plant is to check growth and diminish
fruitfulness, in advanced cases even resulting in death.

_The remedy in greenhouse culture_ is thorough soil sterilization. In
the open field this is impracticable and recourse must be had to a
rotation with immune crops, which will starve out the root-knot. It must
now be borne in mind that the root-knot worm can attack cotton, cowpea,
okra, melons and a very large number of other plants. The only common
crops safe to use in such a rotation in the South are corn, oats,
velvet beans, beggar weed, peanuts, and the Iron cowpea. The use of
other varieties of cowpea than the Iron is particularly to be avoided,
on account of the danger of stocking the land with root-knot.
Fortunately, the disease is serious only in sandy or light soils.

=Rosette= (_Corticium vagum_ (B. & C.) var. _solani_ Burt.) is a disease
of minor importance, which occurs in Ohio, Michigan, and scatteringly in
other states. The fungus causing it (_Rhizoctonia_) attacks the roots
and base of the stem, forming dark cankers. The effect on the plant is
to dwarf and curl the leaves and to restrict productiveness. The potato
suffers more severely from the same trouble. Rotation of crops and
liberal application of lime to the soil are advised for the contr