CXXXVi PROCEEDINGS OF THE ROYAL HORTICULTURAL SOCIETY. 



grows on decaying matter. Mr. Worsdell assigned various causes for the 

 splitting of the fruit. 



Silver-Leaf. — Dr. M. C. Cooke stated that it was doubtful if there was 

 any essential relation between gumming and the so-called silver-leaf 

 •disease of the Prunete. He doubted whether the fungus called Coryneum 

 Beijcrinki had any causal connection with gumming. On the other 

 hand, gumming in Prunun japonica had been traced to Cladosporium 

 epiphyilam. Writing of it in the Gardeners' Chronicle, Dr. Cooke said: — 



" The silver disease of the foliage in species of Prunits has been a 

 puzzle and a mystery for nearly a quarter of a century, and is still almost 

 as mysterious as ever. The leaves retain their normal form, and are 

 neither spotted nor blistered, but are deprived of a large portion of their 

 chlorophyll, assuming a silvery ajipearance, and the whole tree becomes 

 of a sickly habit, and unproductive. No spots or pustules are detected on 

 the leaves, and no fungus mycelium in the tissues, and yet the disease 

 appears to be communicable. 



" The only solution which appears to me to be feasible is, that the 

 present disease is closely allied to the ' Peach-yellows ' of the I'nited 

 States, and possibly a modificaticm of that disease, and should be studied 

 in connection with the literature of that pest. The latest developments 

 seem to indicate that the primary cause is bacteriosis, which demands 

 close and patient investigation. In that case, if proved to be true, the 

 remedy will be almost as far off as ever, since fungicides cannot be 

 effectually applied to such a deep-seated malady. Edwin F. Smith, of 

 the U.S. Department of Agriculture, says that ' at present Peach-yellows 

 seems nearest allied to the phenomenon in plants known as variegation. 

 It is now recognised that variegation (panachure) in many plants is 

 a disease manifesting itself in stunted growth, imperfect assimilation, 

 hastened development, and feeble vitality.' In a note it is added that 

 ' there is also, as in yellows, an abnormal ratio of the ash constituents, 

 both potash and phosphoric acid being in excess, and lime deficient.' 



" There have been several suggestions, and even assertions, that 

 ' Peach-yellows ' is caused mainly by bacteriosis, and this feeling seems to 

 have grown stronger in later years, although in 1S91 ^h. Edwin Smith 

 was of opinion that ' it is almost certainly not a bacterial disease.' If 

 later writers are correct in assuming that the disease is bacterial, there is 

 almost equal j)resumption that ' silver-leaf ' belongs to the same category. 



" What has been said of ' Peach-yellows ' is true also of ' silver-leaf.' 

 ' With our present knowledge, the cure of Peach-yellows appears to be 

 impossible.' All the preventive measures resolve themselves into extir- 

 pation, and can be summed up in two lines : ' The only thing which can 

 be done is to cut out and destroy all trees as soon as any of the signs 

 have made their appearance. It is best to burn the diseased trees, roots 

 and all, if possible.' 



" Both in Pennsylvania and Connecticut, laws are in force to prevent 

 the spread of the disease in Peach-trees known as the yellows, whereby 

 it is enacted that ' it is unlawful for anyone to knowingly or wilfully 

 keep any Peach, Almond, Apricot, or Nectarine-tree infected with the 

 contagious disease known as the yellows,' &c. 



" This, then, is the only remedy which the American Boards of 



