6o DISEASE IN PLANTS. 



brought to light a long list of forms, comprising 

 yeasts, such as Hansen's SaccJiaromyces apicu- 

 latus, fungi and bacteria which live and grow in 

 the soil, finding their water and food supplies in 

 the interstices, and under conditions which we 

 now know to be very diverse. They are usually 

 more numerous, in species and individuals, in 

 cultivated farm and garden soils than in woods, 

 prairies, and untilled lands ; but the geological 

 nature of the strata, the closeness and otherwise 

 of the soil, its damp or dry character and its 

 average temperature (which depends on many 

 things besides latitude or altitude) and other 

 factors co-operate to rule their distribution and 

 numbers. The fact that cultivated land is so 

 well supplied with manures, air, etc., is of great 

 importance in relation to their relative abundance 

 there, and it is extremely probable that the use 

 of artificial manures lessens their numbers con- 

 siderably as compared with land on which stable 

 and other animal manures are employed. 



A list- of the soil-bacteria which have been 

 isolated and more or less carefully cultivated and 

 examined would comprise about fifty species ; but 

 it is certain that, as at present classified and 

 named, many more species are to be discovered in 

 any ordinary soil. 



The fungi are apparently even more numerous 

 than the bacteria, and we may rest satisfied for 

 the present with the general statement that the 

 life-actions of the myriads of individuals of these 

 organisms in the soil completely alter the question 



