10 



On the Diseases of Wheat. 



mildew, rests upon what I consider to be a satisfactory observation 

 made upon a closely allied species ( Uredo rosce) which infests 

 the under surface of rose-leaves. It would be misplaced, in this 

 report to discuss a merely botanical question at great length, but 

 I may perhaps mention that I have satisfied myself by direct ob- 

 servation, that the fungus which first produces the orange- co- 

 loured spores of Uredo rosce, also gives rise to other spores, of a 

 very different form, (which botanists have considered to belong 

 to a distinct genus, and have named Aregma mucronata). I have 

 also met with a review of M. Unger's work ' Die Exantheme 

 der Pflanzen' in the second volume of the new series of the 

 ' Annales des Sciences,' in which it is stated that M. Unger, who, 

 in common with a few other observers, considers many species of 

 Uredo to be morbid secretions from the juices of plants, asserts, 

 that they afterwards change their forms, assuming the appear- 

 ances ascribed to other genera of minute fungi. But surely these 

 plants are too distinctly, too regularly, and too beautifully organ- 

 ized to be the products of disease, like worts or purulent matter 

 in animals. They are also too closely allied to other fungi, which 

 are undeniably true plants, to allow of our considering them in any 

 other light. There are doubtless great difficulties in accounting 

 for the manner in which the minute sporules of these fungi find 

 their way in sufficient numbers within the substance of plants, to 

 produce the effects they do in certain seasons. But, after all, the 

 difficulty of conceiving how this happens, is not greater or so 

 great as that of accounting for the manner in which thousands of 

 minute animals, just visible to the naked eye, sometimes find 

 their way within the very muscles of the living human body. 

 Upon corresponding with the Rev. Mr. Berkeley (who is our 

 chief British authority in this department of botany) he referred 

 me to a paper by Leveille, in the Xlth vol. of the ' Annales des 

 Sciences,' in which Unger's hypothesis is clearly disproved, and 

 these minute fungi shown to be true plants. With respect, how- 

 ever, to the identity of the Uredo roscE, and Aregma mucronata, 

 Mr. Berkeley remarks — It is a point on which I could never 

 completely satisfy myself; for the Uredo seems to be perfected, 

 and drops its spores before the Aregma is produced, or when 

 there are only a few spores remaining. It is, however, certain 

 that several published Uredines are only states of Puccinise (the 

 genus producing the mildew), e. g. U. vincce, U. menthce, &c. 

 The early stage of Puccinia pruni is an Uredo. I have just 

 been examining it." In a subsequent communication, and in 

 reply to my remark that the Uredo was not changed into the 

 Aregma, he observes " I agree exactly with you that the Uredo 

 fully developed never is produced into the Aregma ; and I see 

 the Aregma produced in the way you sketch it, from sausage-like 



