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roots aiut al'e covered with many black protuberances or sclerotia. The 

 disease is caused liy a soil fungus wiucli jienctrates tlie epidernus of tlie 

 root, attackiu.i; and Iircaking down the tissue, wliicli is replaced by fl 

 tangled conipact mass of niycelial threads. The fungus is apparently abl3 

 tc gain entrance iuto auy part of the root, as some infections were found 

 which had started at the crown while others seemed to liave originated 

 in the smaller roots. The outer tissue is first attacked* the mycelium 

 gradiially turning black and giving the root its chanlcteristic Appearance. 

 At this stage the ceuter of the root still retains its natural color, hut in- 

 stead of being compact and brittle is rather soft and watery, while the 

 whole root is tough and pliable. Infected roots which have lain in the 

 soil two or three years gradually become black throughout and finally 

 decay. 



One of the peculiar things about this fungus is that its period of 

 attack is during the winter. Healthy roots with well-formed buds, when 

 set in the fall in infected soil, f.-ul to send up shoots the following spring, 

 and on examination are found diseased with Black Rot, the blackening 

 by this time usually extending one-fourth of the way to the center. After 

 the plants come up in the spring, Avith the return of warm weather, there 

 is no further spread of the disease until the next winter. In working 

 with the fungus in pure culture in the summer, an ice-box is necessary, 

 as it will not grow at the ordinary temperature. 



The organism causing this disease is a new species of fungus belonging 

 to the genus Sclerotinia. The mycelium is septate, branching, and when 

 old becomes more or less blackened. In pure culture it grows luxuriantly 

 on almost any medium if kept at a temperature of 40° Fahr. On nutrient 

 agar or potato agar, sclerotia are produced in three to six days. The 

 sclerotia are at first white compact masses of tangled mycelium, which 

 soon become black on the outside. They are for the purpose of producing 

 the perfect stage and carrying the fungus over imfavorable periods for 

 growth, being able to withstand submersion in boiling water for three 

 minutes without having their germinating power destroyed. I'nder favor- 

 able conditions of moisture and temperature, these sclerotia send out 

 germ tubes .iust as do spores. Under other conditions they may give rise 

 to the perfect stage, although this has never been obtained in pure cul- 

 tures. However, last spring, (1910), the perfect stage' was found in one 



I 



1 Note. — A tecliniual description of tins fungus is to bo published in an early 

 number of Phytopathology by Mr. W. H. Rankiu. 



