592 STATE BOARD OF AGRICULTURE. 



imbedded in a gelatinous matrix which would serve to make them more re- 

 sistant to adverse conditions of environment. When we consider these dif- 

 ferences and the fact that pycnidia also may be produced on the seeds, (Kle- 

 bahn) possibly existing there as immature fruiting bodies capable of later 

 producing spores, it seems extremely likely that, while ordinary conditions 

 of desiccation may be important in kilHng large numbers of superficial spores, 

 there is not enough evidence to conclude that desiccation is effective in en- 

 tirely freeing seeds from the living organism. 



OXYGEN RELATIONS. 



The seat of this disease is near the surface of the soil regardless of whether 

 leaf stalks, crowns, or roots are located at that place. Light is evidently 

 not an important factor in this restriction. Experiments early indicated 

 that the organism is an aerobe. Inoculation to Giltner* H-tubes produced 

 no growth. Broth cultures covered with paraffin oil showed the same re- 

 sults. Very little growth was produced on oatmeal agar in test-tubes when 

 the tops were sealed with paraffin though the volume of air, in such cases, 

 was many times that of the fungus. In tubes of sterile muck, the depth to 

 which the fungus penetrates can be regulated by changing the compactness 

 of the soil. In very loose muck, the fungus seldom penetrates deeper than 

 an inch and a half; in more compact or water logged soil the growth is largely 

 superficial. The same observation has been made in flasks where, in order 

 to get thorough penetration, it is necessary to have the proper amount of 

 moisture and to aerate the soil by shaking the flasks at frequent intervals. 



To determine the effect of introducing large supplies of oxygen, an experi- 

 ment was set up in the following manner: Potted plants, having a well 

 established root system, were allowed to dry to the wilting point. They 

 were then taken from the pots, none of the soil around the roots being dis- 

 turbed, and soaked in water, having a heavy charge of spores. After being 

 placed in 6-inch battery jars and well tamped in with more soil, the entire 

 mass was then drenched with a spore suspension. Glass tubes, bent into a 

 hook so as to deliver air currents upward, were placed in the bottom of the 

 jars and connected with a compressed air reservoir. The amount of air 

 admitted was determined by allowing the air to bubble through water in a 

 wash bottle. An average of about 120 bubbles per minute was introduced 

 for a period of two months. Checks were run where no oxygen was supplied 

 and also where no inoculation was made. When a difference in the size 

 of tops, between the plants supplied with oxygen and the checks, became 

 noticeable, the plants were removed, washed, and examined for signs of 

 disease. Plate VI, Fig 2, shows a picture of a typical plant supphed with 

 oxygen. The roots were attacked at manj^ different points and many of 

 these rotted off two or three inches from the crown ; smaller roots had suf- 

 fered severely and the whole root system was in an advanced stage of decay. 

 The presence of hundreds of pycnidia scattered over the root system fur- 

 nishes proof of the organism causing the destruction. On the inoculated 

 check plants, the disease was produced only around the crown; the roots 

 were as thrifty and as free from disease as in the case of the uninoculated 

 plants. 



This air relation, we believe, explains why a large part of the disease on 

 the roots is near the crown and why roots deep in the soil are very rarely 

 attacked. Excessively high moisture content in the soil, since it drives out 



Giltner, W. Laboratory Manual in General Microbiology, pp. 160-162. New York, 1916. 



