20 
ing, bum the heap to ashes, excavate the soil as far as heated, and re. 
new the fire till the subsoil is reached and the depth of at least a foot 
of soil in all is thoroughly sterilized by heat. 
In many cases, where wood is plenty, dead standing timber to be 
removed, and stumps to be burned, the plan would succeed to stake 
out the field aud build a log-heap at each stake; but if not convenient, 
the annual growth of weeds and grasses, well dried, will furnish fuel 
enough. 
4. Sterile Soils. (Note 11.) 
Among the early settlers of Florida the practice prevailed, when 
planting trees, of digging out the soil to the depth of 2 or more feet 
and filling in around the tree with clay or yellow subsoil obtained from 
virgin land and 3 or more feet below the surface. This plan succeeded, 
in that it surrounded the tree with sterile soil till it formed firm roots 
and a hardened epidermis. 
My investigations show that in infected soils the deep roots are but 
slightly affected in comparison with those near the surface, and that 
the greatest destruction prevails in young trees, nursery stock, and 
plants having surface roots. 
If a tree acquires age and the roots reach deep subsoil, the Auguil- 
lula3 do little damage. Hence the utility of using clay or subsoil, derived 
from virgin forest, around newly-set trees. 
This old plan deserves attention and can be recommended; but since 
the war, in their haste to promote the growth of groves and gardens, 
the later horticulturists reverse this method, imbed the young tree in 
surface soil, and use nitrogenous fertilisers to encourage rapid develop- 
ment, this certainly causes increase of the root-knot. 
5. Disuse of Land. 
Keeping land clean, free from all growth for two or more years, has 
proved of great benefit if done before trees are planted. I believe the 
worms require living tissues to develop in, and deprived of this they 
would die, probably within the limit I have given. 
In many places where the soil has not been cultivated for a long- 
series of years, and the Broom Sedge Grass has exterminated all other 
weeds, I have failed to find any traces of the Anguillula, and I regard 
this as confirmatory proof that disuse of land prevents the root- knot. 
6. Disuse of Easily Infected Crops. 
In most of our Southern States, where the Clovers and Buckwheat 
will not prosper, it has been the almost universal custom to substitute 
the Cow-pea as a soil-renovator. Drilled or broadcast it is the great 
crop for 'Maying by" corn, and as a second or third crop after rice, 
oats, or market garden. Very few groves or orchards but have annu- 
ally from one to three crops of pea-viues plowed in for fertilizing. 
