76 DISEASES OF GINSENG. 



CHAPTER XXI. 

 DISEASES OF QINSENQ. 



Damping Off of Seedlings, 

 (rhizoctonia sp.) 



(BY prof. JAMES M. VAN HOOK.) 



Rhizoctonia is termed a sterile fungus, since it does not pro- 

 duce spores in the ordinary manner. It may be distinguished, 

 however, by the vegetative part, if placed under a microscope. 

 The branches of the threads are divided by cross-walls near the 

 point of union with the thread (Fig. 27). At this point also, the 

 branches are usually slightly constricted, especially in the young- 

 er threads. These are frequently hyaline and vacuolate. 



For more than a decade, RHIZOCTONIA has been known 

 in this country to be the cause of plant disease. Experiments have 

 proved it to he often purely parasitic. Among the diseases pro- 

 duced by it is that of "damping off," where it destroys seedlings. 

 Some of the plants it is known to attack are ornamental asparagus, 

 china aster, bean, beet, carnation, carrot, celery, cotton, lettuce, 

 potato, radish, rhubarb, sweet-william, and violet. 



When affected with this "damping off" fungus, the plants 

 often fall over, making a bend at the surface of the soil, as shown 

 in (Fig. 28). When attacked below the surface, the plants wilt. 

 Specimens of this fungus were brought from a ginseng garden by 

 Professor Atkinson in June. These were taken up with a quan- 

 tity of the soil, so as to preserve them in as natural a condition as 

 possible. Fungus threads in and around the affected parts of the 

 stem, when placed under a microscope, present the appearance 



