92 ON A PECULIAR FORM OF MILDEW IN ONIONS. 



of the bulb, acquires a sickly hue, which rapidly increases : the 

 leaves wither ; the roots decay, and are covered at their junction 

 with the bulb with a filmy mucedinous web ; the bulb itself 

 ultimately becomes loose from the destruction of the roots, and 

 as the mould spreads entirely decays. In other instances a pla- 

 centaeform Sclerotiiim is formed at the base of the bulb, of 

 greater or less size ; while in other instances, again, the whole 

 substance of the bulb and neck is impregnated with mycelium, in 

 the midst of which appear multitudes of little black seed -like 

 grains, which have been described as Sclerotium Cepse, Lib. ;* 

 and specimens have been published under that name in the 4th 

 Fasciculus of British Fungi. Still other forms of mildew occur, 

 but it is to this latter that my attention has been more espe- 

 cially directed. 



The dry summer of 1847 was in many districts extremely in- 

 jurious to the onion crops. AVhole breadths at once became dry 

 and withered, frequently not from the presence of any disease, 

 but from mere lack of moisture, and the bulbs were extremely 

 small and insignificant. Mildew also was very prevalent, and 

 various examples were forwarded to Dr. Lindley ; some of which, 

 and amongst them the form under consideration, were placed in 

 my hands for examination. I happened at the time to be staying 

 at Margate, where my friend Mr. G. H. Hoffman, with the as- 

 sistance of a good compound microscope, had been making some 

 observations on the mycelium of the parasitic fungi which attend 

 or produce mildew, and I was glad of the opportunity of exa- 

 mining the present parasite with him. The specimens were 

 somewhat decayed, in consequence of having been some time on 

 the road, and their odour was extremely disgusting. On making 

 a section through tlie plant, every part of it was found to be 

 more or less decomposed, and filled with white mycelium, which 

 was occasionally greenish from the juices of the matrix ; amongst 

 which appeared the Sclerotium^ in various stages of growth, 

 distinguished in the younger specimens by its compact substance, 

 and in the older by the dark blackish cuticle. It was a matter 

 of importance to ascertain, if possible, what was the nature of 

 these globular bodies ; and the manipulation applied by Mr. 

 Hoff"man to the observation of mycelium in other cases ap- 

 peared likely to lead to some positive result. 



Leveillef has, in his interesting memoir on the genus Sclero- 

 tium, combated the pretensions of the substances comprised under 

 that name to occupy a place amongst autonomous fungi ; and, 

 though his observations are as conclusive as the nature of the 

 case would admit, without an experiment like that now recorded, 



* Libert, Plantse Cryptogamicse Arduennce, No. 238. 

 f Annales des Sciences Naturelles, 2^''^ Se'rie, vol. xx. p. 218. 



