WORN-OUT LANDS 



87 



demonstrated by the Department of Agriculture, is 

 not a new one. Lindley wrote, in 1839: "One 

 function of the root bark is to give off such superflu- 

 ous matter as it is necessary for its health that the 

 plant should part with. If roots are so circum- 

 stanced that they cannot constantly advance into 

 fresh soil, they will, by degrees, be surrounded by 

 their own excrementitious secretions." 



Virginia has a large area of worn out tobacco 

 lands, which have been so constantly used they 

 yield no longer. No amount of concentrated fertil- 

 izer will induce the growth of tobacco. These lands 

 are often rich in humus and in good physical con- 

 dition, producing an abundance of other crops. 

 Their behavior points to the conclusion that to- 

 bacco has been grown so continuously its excreta 

 has saturated the soil and is poisonous to that plant. 

 We know that in power of absorption rootlets can- 

 not discriminate digesting toxic solutions readily; 

 and that plant fluids enter through membranes very 

 near the root tips, newly formed wood throwing off 

 an impenetrable bark as they extend, the corky 

 cover protecting fibre from poisonous substances. 

 We also see that roots continually excrete injurious 

 solutions, for no one is able to make grass grow on 

 the drainage side of large trees, though he furnish 

 never so much sunshine, air and artificial fertility. 



This question may be considered a digression 

 from the subject of fig culture, but it is at the basis 



