106 



PROTECTION OF PLANTS, 1921-22 



the affected stems abundant sclerotia were found in the place of the pith. 

 These are well shown in Fig. 1-A. 



These symptoms are not the first, while conducting experiments in the 

 green house, with potato and tomato plants, I have discovered their precedents. 



The first signs of the disease are patches of whitish mycelium on the outside 

 of the potato or tomato stem at the point of infection at the surface of the 

 soil, where the natural infection ordinarily takes place. If the weather is 

 humid profuse mycelial growth occurs with the later development of external 

 sclerotia. At first these are whitish, turning black and finally falling to the 

 ground. At the same time the mycelium gradually penetrates the inner 

 tissues reaching to the pith. In the pith rapid growth takes place with the 

 formation of internal sclerotia. 



Fig. 1. — Sclerotia in pith of potato stem. 



Cultural Characteristics 



The sclerotia, after being frozen for a month, sterilized in 1: 1000 solution 

 of mercuric chloride and washed in sterile water, develop profuse mycelium 

 but in no case was an apothecium observed. 



The mycelium develops more rapidly on sterile carrot than on potato or 

 oat-meal agar. The carrots were first covered with a white mass of mycelium, 

 which gradually turns brown and then black, forming a solid mass of sclerotia 

 on the surface, shown in Fig. 2. 



