19 



treatment with preparations of this nature is not to be considered, 

 as it is ineffective if the smaller quantities are used and its cost 

 prohibits the use of large amounts. 



Although the use of lime for this disease promised little, still it 

 had the advantage of being very cheap and readily procured be- 

 sides being often useful in its effects on the physical condition of 

 the soil. Moreover, if it is even of small merit in combating the 

 disease it is to be recommended, as, being already familiar to the 

 planters, they would use it in preference to other more effective but 

 less common materials. The good results obtained from its use in 

 these field experiments may be partly due to the disinfecting action 

 of the heat of slaking and possibly, also, to lessening the amount 

 of vegetable matter in the soil which could be used by the fungus 

 as food. That the heat generated by slaking may have had some 

 fungicidal effect is further indicated by the fact that when the 

 already slaked lime was used in the form of a thin paste at the 

 rate of 200 grams per square meter on a much-diseased plat of 

 Petiveria no effect in checking the progress of the fungus was to be 

 observed. The use of air-slaked lime is not to be recommended in 

 the case of the black root disease if it is wished to check the disease 

 at once by its application. Its effect will be good only as it tends 

 to improve the soil and hasten somewhat the decomposition of the 

 vegetable matter on which the fungus feeds. Such action in any 

 event will be slow. 



The good results from the use of sulphur must be referred to its 

 fungicidal properties. In well-aerated soils sulphur dioxid is prob- 

 ably formed, and hydrogen sulphid in soils excessively moist. Both 

 of these substances have weak action as disinfectants. But it is not 

 unlikely that their continuous production through several months 

 would serve at least to prevent the growth of the fungus and perhaps 

 to destroy it. Additional evidence that some such action exists was 

 obtained by mixing sulphur in the soil with which a trench about 

 4 inches deep and of equal width was filled, using about 15 grams 

 of sulphur to each meter of the trench. The fungus has killed the 

 plants up to the sulphured soil, but during the entire year on which 

 it has been observed has not passed to the healthy plants on the other 

 side. In part of the ditch which received no sulphur the fungus has 

 passed over and destroyed the Petiveria plants. 



In the three years since this work was begun 2 per cent, or 6 out 

 of 317, trees have died in the treated plats, all of these being in the 

 plats receiving the smaller applications of sulphur and chloronaph- 

 tholeum. None have died in those treated with the other disin- 

 fectants, but the results from the treatment with these substances 

 are of little interest because of their cost. In the check plats which 

 were merely cleaned and ditched 5 per cent, or 16 out of 334, trees 



