iv.] NEW DISEASE OF POTATOES. 21 



common on all decaying vegetable matter when no 

 Sclerotia are present. No one can tell for certain, by 

 mere examination, what any given Sclerotium will produce 

 on germination. Sometimes a clue is given to what a 

 Sclerotium may possibly produce by observing its habitat. 

 For instance there is one Sclerotium named S. fungo?um, 

 P., commonly found in dead examples of certain members 

 of the mushroom tribe, chiefly found under the gen era named 

 Agaricus and Eussula, and sometimes inside the large decay- 

 ing corky fungi, named Polyporus, of trees ; these Sclerotia 

 invariably produce a small mushroom-like fungus named 

 Agaricus tuberosus, Bull. A closely allied Agaric, named 

 A. cirrhatus, Sch., also springs from a not dissimilar 

 Sclerotium. Another and very small Sclerotium found in 

 decaying onions and named S. cepcevorum, B., produces a 

 minute mould named Mucor subtilissimus, B. It com- 

 monly happens, however, that Sclerotia may be found on 

 the surface of the ground near where the supporting plant 

 has decayed. When gathered from such positions it is 

 impossible to say what they will produce under culture, 

 and sometimes they so closely resemble small truffles 

 (which, too, are often found on the surface of the ground), 

 that without a microscopical examination it is impossible 

 to distinguish one from the other. The perfect state of 

 some Sclerotia is unknown, as S. stipitatum, Fr., found in 

 the nests of white ants in India. 



When the large black Sclerotia were found in Irish 

 potatoes they appeared to us to differ from the Sclerotia 

 we had hitherto noticed, and although it is never safe to 

 guess at what an unfamiliar Sclerotium may produce, yet 

 in our printed report, published in the Gardeners' Chronicle 

 for 20th August 1880, we hesitated to refer the bodies to 

 any already described form of Sclerotium. Sclerotia are by 

 no means uncommon in herbaceous stems, in cabbage 

 stumps, and even in potato stalks ; but the new bodies did 

 not appear to us to be the same with any others we had 

 previously observed. Black Sclerotia are not uncommon 



