Sick Soils 23 



3-4 septate, the microconidia are one celled, minute 

 spherical to elliptical. 



Soils Rendered Sick by Certain Forms of 

 Animal Life. Some soils are made sick by the 

 presence of minute forms of animal life. A striking 

 instance of this is the root knot, a disease produced 

 by a little worm generally known as nematode, or 

 eel worm. 



Root Knot 



Caused by Heterodera radicicola (Greef) Mull. 



Although root knot is most prevalent in light soils, 

 it may sometimes be found in heavier lands. The 

 trouble is most widespread out of doors in the South- 

 ern States, where the winter is mild. In the North 

 the worm is usually unable to winter over in the 

 open unless it is protected by trash or dead weeds. 

 It is, however, prevalent in greenhouses and is un- 

 doubtedly introduced with sick soil brought in from 

 the field. 



Symptoms. The disease is characterized by swell- 

 ings or knots on the roots. These swellings may be 

 variously shaped, and are often mistaken for the 

 true nodules of legumes (fig. 22.). Infected plants 

 become stunted, pale, and usually linger for a long 

 time before dying. 



The Organism. The nematode is a very minute 

 worm, seldom exceeding one twenty-fifth of an inch 

 in length. It is semi-transparent so that it cannot 

 be easily detected by the naked eye. In searching 

 for the eel worm, it is necessary to break a fresh knot 



