ON A PECULIAR FORM OF MILDEW IN ONIONS. 93 



which alone could furnish the means of seeing- the actual deve- 

 lopment of the fungi from the mycelium of which they are so 

 many anamorphoses, they require some direct confirmation, which 

 does not, however, at all detract from their own original merit. 

 It became, therefore, a matter of interest to embrace the oppor- 

 tunity now offered of following up the point. 



It is well known that it is possible to watch many mucedines 

 from the first germination of the spore to the complete develop- 

 ment of the fructification, by simply placing the reproductive 

 bodies in a drop of water on a slip of glass, covering it with a 

 piece of microscopic glass, and luting the edges with wax to 

 prevent evaporation. The mycelium is developed in the water, 

 while the fertile branches make their way into the surrounding 

 stratum of air, and bear fruit. It was determined to subject a 

 portion of the mycelium from the tissues of the diseased onion, 

 and a portion of the sclerotium, to this process. In one slip of 

 glass our success was complete, in the others more or less per- 

 fect. A single observation, if possible, should not be relied 

 upon. An extremely thin slice from the stem was taken, so thin 

 as to enable us to distinguish easily the several parts of which 

 the object was composed. The cells and vessels of the matrix 

 were well defined, and the mycelium connected evidently with 

 the sclerotioid granules, which were separated from each other 

 by veins of flocci, very much in the same way in which sporangia 

 of certain fungi are combined. It was easy also to recognise 

 the structure of the Sclerotiiuii as well externally as internally. 

 The inner tissue was found to be not compactly cellular like that 

 of Sclerotium durum, complanatuin, &c., but filamentous, as in 

 Sclerotium Boletorum, Corda, consisting of closely interwoven 

 branched threads resembling on a small scale. the tissue of the 

 seed-pods of Fucus vesiculosus. This structure, it is obvious, 

 made it more easy to trace the continuation of the mycelium 

 from the tissue of the Sclerotium. 



After the expiration of a few hours the slices began to assume 

 a different appearance, from the elongation of the mycelium, 

 which was protruded on all sides, and was branched and Hexuous. 

 Some portions were repeatedly articulated, others either entirely 

 without articulations, or with merely one or two scattered dissepi- 

 ments. As long as the mycelium was confined to the drop of 

 water, there was no appearance of fructifiication, and even the 

 tips of the filaments were scarcely incrassated. There was not, 

 then, the slightest iutimation to what genus of fungi it belonged ; 

 but no sooner had it penetrated through the globule of water 

 into the surrounding air, than a marked change took place. The 

 tips of the short lateral branches became incrassated, and at 

 length globose, and contained a grumous mass, which soon mani- 

 fested definite spores ; shortly after which the vesicle burst, and 



