May 15. 1919 Influence of Soil Environment on Rootrot of Tobacco 81 



It contained 3,200 gm. Other pots were now filled with 2,900, 2,600, 

 and 2,300 gm. of soil, four pots of each degree of compactness being used. 

 Two pots of each series were steam-sterilized. Connecticut Havana 

 tobacco was then transplanted into them. To avoid any abnormal con- 

 ditions due to transplanting, especially in the compacted soils, which 

 were so hard that a knife could scarcely be inserted into them, a small 

 amount of soil was taken out of the center of each pot with a cork borer. 

 The hole was filled with uninfested loose soil, and the young plants were 

 transplanted into it so as to give all an equal chance to start. 



The results were very interesting. The plants in the sterile com- 

 pacted soils did very much better than was expected, although the 

 loose soils were much more favorable to growth. In the infested soil, 

 however, the plants in the compacted soil made no growth whatever 

 (PI. 5, IV). Examination of the roots showed that in the loose infested 

 soil comparatively few lesions occurred, and the taproot was present, 

 while with increasing compactness the taproot was lost, and gradually 

 increasing numbers of lesions occurred. 



The experiment has an important practical bearing on the preparation 

 and cultivation of tobacco soils infested with T. hasicola. Anything 

 which can be done to avoid, or remedy compactness or baking of soils 

 will no doubt lessen the disease even in badly infested soils. In other 

 words, soil in good tilth is less likely to be heavily damaged by T. hasicola 

 than soil in poor tilth. 



TRANSPLANTING DISEASED SEEDLINGS 



The influence of the use of diseased seedlings, for transplanting to the 

 field is not strictly an environmental feature of the problem. It relates, 

 however, to the amount of infestation in the soil and has a very impor- 

 tant practical bearing on results obtained under field conditions. It is, 

 furthermore, a point upon which some contradictory evidence has been 

 obtained by various experimenters, especially Benincasa (j), Gilbert 

 {12), and Clinton {8). The results already presented, especially in 

 regard to the influence of soil temperature, may serve to explain the 

 variation in results from year to year, or of the recovery of infected 

 transplanted seedlings. This is, however, apparently not the only 

 explanation. The writer has shown that varieties of tobacco and even 

 strains, vary in their resistance to rootrot (14). Transplanting healthy 

 plants to infested soil under favorable enviro^imental conditions for dis- 

 ease is shown to result in marked differences in yield of the different 

 types used. 



It is known that the tendency of diseased plants is to send out new 

 roots to replace those lost by disease. Transplanting diseased plants 

 consists practically in infesting a small area of soil surrounding the base 

 of the plant with T. hasicola. Part of the new roots, especially those 



