Dec. io f 1913 
Foot-Rot of the Sweet Potato 
263 
potatoes in storage. In the locality in which this disease occurs, the 
hotbeds are started about April 1, or even sooner, so that infection of 
young plants might easily take place from pycnospores that had endured 
as late as May 20. In old fields the beds are often made from the soil 
on which sweet potatoes have been grown the previous year, thereby 
providing the best conditions possible for direct infection of the new 
crop. Furthermore, it was previously pointed out that the foot-rot 
organism spreads from diseased stems to the potatoes and develops 
pycnidia thereon. Experiments have also shown that under hotbed 
conditions the organism will grow from diseased potatoes on to the slips 
produced therefrom. Therefore, owing to the comparative obscurity of 
diseases of this type, infected roots might readily be overlooked when 
selecting seed, thereby making the sprouts growing from such potatoes 
liable to infection. 
The brown, spherical, thick-walled, chlamydosporelike bodies were 
found in abundance embedded in the cortex of diseased parts of plants 
wintered out in the wire cages. What function these forms have is not 
yet known, although it is possible that they are able to reproduce the 
fungus and serve to carry the organism through unfavorable conditions. 
Repeated attempts, however, to germinate them have always given 
negative results. 
SOME PHYSIOLOGICAL CHARACTERISTICS OF THE FUNGUS 
CHARACTER OF GROWTH ON DIFFERENT CULTURE MEDIA 
The foot-rot fungus grows well on some kinds of media, but Sparsely 
on others. The growth on some media may be regarded as character¬ 
istic of the organism and is unlike that of any other fungus with which 
the writer is familiar. 
A comparative study of growth has been made on nine different cul¬ 
ture media—i. e., corn meal, string-bean agar, string beans, Irish-potato 
cylinders, sweet-potato cylinders, sweet-potato stems, rice, beef bouillon, 
and beef agar. These different media have not been selected for any 
particular reason, except that they are those commonly used and can 
easily be duplicated. Five tubes (flasks in case of com meal) were 
inoculated on November 25, 1912, with conidia from a 25-day-old cul¬ 
ture grown on com meal. The tubes and flasks were kept in the light 
on a table in the laboratory, the temperature of which varied from 18 0 
to 24 0 C. They were kept under observation until January 31, 1913, 
after which, owing to the dried condition of the cultures, no more notes 
were made. The following records, given in number of days from the 
beginning of the experiment, show the nature of the growth on the 
different media. 
