6O FARM DEVELOPMENT 



one per cent. This strength of solution has been found 

 strong enough to kill the alga without injury to the fish, 

 while a solution a few times as strong would cause the 

 fish to thrive so poorly as to cause loss rather than gain 

 from their culture. 



Those who have given this matter most study believe 

 that, in respect to many plants, minute amounts of sub- 

 stances poisonous to them or to certain other plants, are 

 either given off by their roots, yielded by their decaying 

 products or supplied by bacteria associated with their 

 roots; while, as in the case of the fish, there are still 

 other plants which they do not affect. As the reputation 

 for honesty or dishonesty of the manager of a savings 

 bank may cause the institution to prosper or decline, so 

 it is believed those minute substances often cause profit 

 or loss from the fields. This theory has not as yet been 

 placed wholly in harmony with the generally accepted 

 theory as to the function of manures and commercial fer- 

 tilizers as so much available plant food added to the soil. 

 Presumably when more is known of the soil and how 

 plants feed, both the old and the new theories will be 

 brought into harmony. The fact that wheat does well 

 after corn, but often does not yield so well after wheat 

 or oats, and that crop rotation often increases the 

 production of all the crops in the rotation over a long 

 series of years, cannot be so fully explained as by ac- 

 cepting the theory of toxic soil substances, along with 

 the theory of the stimulation of the crops by feeding 

 them with yard manure or commercial fertilizers. 



With the peaty soils there is an over-abundance of 

 vegetable matter. The question with these soils often 

 is, how to enrich them in mineral substances. Care must 

 be taken to prevent peaty soil from being burned too 

 deeply, since once the surplus water is drained out of 

 peaty lands, they become dry and will burn if set on 



