16 DEPARTMENT OF AGRICULTURE

talaria spectabilis proved to be one of the most interesting plants
yet studied in its host-parasite relationship with root-knot nematodes.
It was observed that the root tips of growing specimens are invaded
by large numbers of larval root-knot nematodes, but up to the pres-
ent time not one larva has ever been found to have reached the adul
stage. They all appear to perish at a very early stage of fixation in'
the root. This legume is therefore an excellent trap plant and cover
crop combined. On the basis of greenhouse and field experiments i
has been found very effective in cleaning infested land of root-knot
nematodes. In entering the roots the nematode appears to be able to
induce the root tissues to produce the so-called giant or nectarial cells
on which they feed, but for some reason the nematodes will not gro
to the adult stage and produce eggs and progeny. However, even in
this case the plant suffers from an invasion of its roots by these nematodes
larvae; this is shown by the fact that small seedlings of C. spectabilis will
die or at least appear sick for a time after invasion. Eventually theq
plant will recover. Solanum grandiflorum R. & P., a weed growing inq
Brazil1 and used there as a root stock for tomato grafts on root-knot-I
infested lands, exhibits characteristics quite similar to those of Crota-
laria spectabilis in its relationship to the root-knot nematodes. Here,|
too, the roots are invaded and their tips blinded by the larval root-knot
nematodes which again are unable to grow and develop as they become
fixed. The Solanum eventually will also attract from the soil larval speci-
mens of the nematodes but will recover after their invasion and death.
Here again the young seedlings may suffer badly from this invasion and,
in fact, may even be killed. Of a total of 100 seeds planted in root-knot-
infested soil only three seedlings survived while a control planting from I
the same lot of seed in sterilized soil gave full germination and only
healthy growth.
 Still another variation in host-parasite relationship is shown by the |
rose geranium (Pelargonium graveolens [Thumb] L'Herit). In this
plant the roots also appear to possess considerable resistance against |
attack. Few galls are formed, many of which are empty, and only occa-
sional ones were observed with egg-laying females. In contrast to this
behavior of the roots, the basal portion of the stem appears to be very
attractive to root-knot nematodes and consequently is invaded by large
numbers, galls being formed and female specimens being able to grow
to maturity and produce eggs (Fig. 10).
 We are convinced that a study of the numerous host plants affected
by root-knot nematodes, including the so-called resistant and immune
types, will bring to light additional information of much value for a
better understanding of these numerous and complex host-parasite inter- I
relationships. These are all matters of not only theoretical interest, but

 1 For the opportunity of studying this plant we are indebted to S. B. Fenne of
the Institute of Inter-American Affairs. .