81 



disease, as is shown by the susceptibihty of certain plants to 

 rust and mildew. 



On the other hand, a lack of soil moisture induces weakness 

 and renders the plants more susceptible to disease. An excess 

 or insufficient amount of soil moisture causes prematurity and 

 affects the life cycle of certain pathogenic organisms. 



The stimulating effect of electricity, fertilizers, and sterilized 

 soil often proves injurious by developing a too high water content 

 in the tissue and rendering the plants more susceptible to disease. 

 .Sterilized soil has a stinuilating effect on many crops, and if 

 grown under ordinary tep.iperatures they mature some weeks 

 earlier than those grown in unsterilized soil. Such crops, how- 

 ever, are likely to be more or less flabby in appearance and 

 generally contain a higher water content of the tissue than nor- 

 mally grown plants. Similar results are to be seen in connection 

 with electrical stimulation. 



An excess of nitrates in the soil inhibits root absorption and 

 induces wilting, and in some cases causes malformations from 

 on overabundance of plant food. 



An unsuitable soil texture develops the plant abnormally and 

 susceptibility to disease is increased. Tillage, irrigation, mulcli- 

 ing, etc., are important factors in securing vigorous plants and 

 exerting a beneficial influence as regards susceptibility. 



\\'hile there are certain external factors associated with en- 

 vironment w'hich induce pathological conditions in plants, in the 

 majority of cases it so happens that more than one factor is 

 concerned in bringing about this diseased condition, and similar 

 abnormal conditions may be produced by dift'erent causes. 



In conclusion, it may be said that in most cases, if not all. 

 vital depressions are the real cause of disease. These are brought 

 about by the abnormal conditions which modify and reduce the 

 power of resistance, consequently the organism falls a prey to 

 the ever-present germ. 



CONCLUSIONS 



Tomatoes are subject to various diseases, some of which are 

 common to outdoor plants and others confined to those grown in 

 greenhouses, and many affect crops grown under either condi- 

 tion. 



The methods of treating outdoor crops necessarily differ from 

 those required inside, since in the latter case the environment is 

 more or less under control, and by proper control of the environ- 

 ment most of the diseases ma}^ be eliminated. 



The principal diseases affecting outdoor tomatoes are the 

 blossom end rot, tomato scab (Cladosporium), anthracnose 



