180C5.) On Siberian Wheat. 309

plant. R. W.'s opinion is not very different. Sir Joseph Banks 8ays they are occasioned by the farina of 4 parasitic füngus gaining admission into the pores of the Straw; thus accounting for their formation in a way S0 different from the theory of R. W., that there is Some reagon to believe hat the latter writer does not consider atmospheric influence as the cause of blight upoz the hypothesis of the former,

If 1 am notmistaken.* however, Sir Joseph Banks observes, thatthe want of logomotion in plants, is Supplied by pores, or mouths, on the Surface of their leaves ä4nd Stems, for the admission of air and moisture; that they are very open in wet, and close, or nearly so, in dry weather; that the gur- faceof Straw contains alternate Stripes, the one Set pretty firm and of a close texture, and the other with mouths; and that the latter are often penetrated by the farina of a small fungus, with sprouts, and intercepts part of the Sap in its ascent for the Support of the grain. Now, as this farina enters the stalks of the corn only when the pores are much opened by rain and dews, it is obvious that the gtate of the weather or air is the Primary-cause of mildew, under tiie hypothesis of Sir Joseph Banks, as well as under the theories ot R, W. and Mr. Lawrence.

I can better Support these theories by facts, and various phenomena, than| can uphold the opinions of Sir Joseph Banks. This is not cConSolatory, for under the former we have reason to doubt tbe posSIbility of prevention, while the latter afford 5ome room to hope for a remedy. On this SCOre, how- ever, I must confess that I am not very Sanguine,

We are informed by Sir Joseph, thal the fungus attacks corn early in the Spring; that it is at firstof an orange, and afterwards of a dark brown colour, when in hol weather, it ripens and Sheds itsSeed in 5o Short a time as one week; that the rust, in the orange coloured State may be obszerved in the Spring upon a few stalks of corn in a feld; and that in this Stage, it 18 many weeks of Coming to many? Fehis ünz terval, therefore, he adviges theagriculturist to destroy those infected plants--the Seeds of innuwerable fungi. He adds that each pore may contain 20 to 40; that each fungus Sheds 100 Seed; and that in hot weather, they ripen 50 Soon that a single stalk may infect a whole pariseh. He likewige States that it way be conveyed in the Straw of mannre„ufhat Several Sorts of grass are Sübject to it; and that the barberry busb, which is well known to bear a rust resembling that on corn, Sheds the farina ofits fungus, which is Spread by the wind amongst the Stalks of wheat.

* I cannot at prezent refer to this Pamphlet.