450 



layers. When a portion of tlie white mold fonnd on the leaf is trans- 

 ferred to a microscopic slide, and viewed by a power of about one- 

 eighth, i^ appears as at 1, Fig. 18. The spores seen on the ends of 



the branches are compound, 

 and when moistened, resolve 

 themselves instantly into 

 separate sections (2.) When 

 the mold is matured, view- 

 ed by a power of about 

 75 diameters, it apx)ears dou- 

 ble-fruited, as at 5 and 6. 

 It is believed by the farmers 

 at Swamp SCO tt, that dry 

 weather favors the growth of 

 the white mold, but that 

 moist and rainy weather fa- 

 vors the growth of the black 

 fungus, or rot, which is seen 

 mostly on the bulb of the 

 onion. When the black spores 

 are viewed by a power of 

 about one-eighth, they appear 

 of a rosette form, (3,) each 

 resembling a combination of 

 cells, encircling a common 

 center. Figure 19 represents at 7 a highly magnified view of a portion 

 of the leaf of a mildewed onion ; 8, a chain of elliptical spores, which 

 grow in great profusion over it, when the leaf is kept in a moist con- 

 dition for a few days j 9 shows stoma1.es of the leaf from which thread- 

 like mold, mycelium, is seen to proceed, proving that the fungus has 

 ramifications under the epidermis, and doubtless through the intercell- 

 ular spaces, if not through the cellular substance itself, from which the 

 fungoid threads draw nourishment for the support of their fruit, &c. 

 I subjected the black spores (3) to the action of concentrated nitric, nitro- 

 muriatic, and sulphuric acids, caustic, potash, and lime, for twenty-four 

 hours, without effecting any change in structure. When immersed 

 eigbit days in uitro-muriatic acid, the spores become slightly bleached, 

 and apj)ear as at 4. When immersed in heavy oil of tar, which contains 

 a laige portion of carbolic acid, their structure is materially changed. 



In an address delivered by Mr. Ware before the Essex Agricultural 

 Society, at Newburyport, September 29, 18G9, he said that " The onion 

 blight and smut is at times very destructive to the onion crop, turning 

 the most promising fields in a few days to scenes of desolation, which 

 is caused, in my oi^inion, by a paras'itic plant, growing uj)on and con- 

 suming the vitality of the onion. The onion smut so impregnates the 

 laud with its spores, as to render it unsafe to plant onions for several 

 years on laud thus affected. White blight comes upon the crop at the 

 period of its most vigorous growth, in a dry time, showing its effect 

 perhaps in a small spot at first, but, in case the dry atmosphere con- 

 tinues, r;:i'id]y spreading over the whole field. Two or three days give 

 sufficient time to stop entirely all future growth of the crop, unless a 

 change in the weather occurs unfavorable to the growth of the parasite." 

 When an onion aiiected with fungus is placed in a vessel with a few 

 drops of water and exposed to a temperature of about 75°, its decay is 

 hastened very materially, but apparently more from the presence of 

 infusorial life than from the parasitic fungi. The latter seem to prepare 



