CH.V.] FUSISPORIUM DISEASE OF POTATOES. 31 



occurs in more than one form. One condition of the pest, 

 named Periola tomentosa, Fr., was described in 1836 as 

 an assailant of potatoes in the midland counties by the 

 Rev. M. J. Berkeley. This form is probably no other 

 than masses of compacted villons mycelium or spawn, 

 from which the Fusisporium at length arises. Another 

 and early condition of Fusisporium Solani, Mart., was 

 also described by Mr. Berkeley under the name of Dacty- 

 lium tenuissimum. A. distinct rose-coloured species of 

 Fusisporium, named F. roseolum, Steph., also grows on 

 decayed potatoes. 



Fusisporium Solani, Mart., is not peculiar to decaying 

 potatoes, for it grows with rapidity on potatoes which are 

 apparently undiseased, if bruised or cut. To the unaided 

 eye its growth bears such a close general resemblance to 

 Peronospora that it might readily be mistaken for it ; 

 indeed, the use of a lens, even with practised observers, 

 is often necessary to distinguish between the two. The 

 fungus is simple in structure, and consists of threads and 

 compound spores ; the spore- bearing threads springing 

 direct from a floccose, sometimes mucilaginous, bed of 

 spawn or mycelium, as illustrated at A, Fig. 10, enlarged 

 400 diameters. The fruiting threads carry spores attached 

 somewhat obliquely, as illustrated at B, but more clearly 

 seen in .Fig. 11, where they are enlarged to 1000 dia- 

 meters. The spores are spindle-shaped that is, attenuated 

 at both ends ; and curved like a crescent : each spore, at 

 first simple, is at length furnished with about three joints 

 or septa, and each of the four pieces of the compound 

 spore exhibits one or more lustrous spots. Sometimes 

 all four parts of a spore germinate whilst still attached to 

 the supporting threads, as at C, Figs. 1 and 1 1 ; but it 

 often happens that at maturity the spores fall into four 

 pieces, as at D, Fig. 11, and each of the fallen pieces 

 sometimes germinates at once. This rapid germination, 

 by its extension of the parasite, accelerates the destruction 

 of the host plant. The fallen pieces of the spore are at 



