184 The Scottish Naturalist. 



THE POTATO SCLEROTIET. 

 By A. STEPHEN WILSON, C.E. 



WHAT is a Sclerotium ? The best known and most easily 

 found sclerotium, is the one called Ergot, — the sclerotium 

 of Claviceps purpurea, Tul. Its structure can be fully determined 

 only by watching its growth from the earliest stage up to maturity. 

 In the earlier stages this body is quite white, and is seen to consist 

 of an interior axis of sponge-like mycelium, enclosed in enormous 

 numbers of small oblong spores. These become agglutinated 

 around the axis, and the whole gradually assumes a dark purple 

 colour. Another sclerotium which is very easily found in April on 

 dead leaves of turnips and other plants, is that of Typhula incar- 

 nata. This also is at first perfectly white. It may be found be- 

 low the snow in February upon dead leaves, of a size little more 

 than visible to the naked eye, and it gradually grows to the bulk 

 sometimes of a tare seed, and is of a brown colour. But the struc- 

 ture of this sclerotium is not the same as ergot. It originates on 

 the point of a line of mycelium. This line begins to branch, and 

 the branches immediately begin to branch; and the ramifi- 

 cation is so close, that the lines of mycelium, instead of running 

 away out into a loose web, form a solid ball. In this case there is 

 no axis, and there are no spores. In some other sclerotia the mass 

 is hollow in the interior, with many loose lines of mycelium 

 pointing inwards. 



It is thus evident that all sclerotia, admitted as sclerotia, are not 

 formed on the same plan : so that if a small body is found in the leaves 

 and tubers and haulms of the potato, bearing some resemblance to 

 the sclerotium of Typhula incarnata, there is no great impropriety 

 in calling it a sclerotium until the theory of its existence has been 

 worked out. But the body which has actually been found in the 

 potato tissues, and most perfectly developed in the leaves, is so 

 small compared with other sclerotia, that there seem some 

 propriety in calling it a sderotiet, to indicate its microscopic di- 

 mensions. 



Considerable controversy has taken place as to the structure of 

 this minute body. When the statement was first made that this 

 little ball was the sclerotium from which the mycelium of Peronos- 



