NOTES ON RECENT RESEARCH. 



718 



plasma remaining at the apex of the spore. The projections on the 

 outer side of the exospore are formed in S. emiliana before the separation 

 of the two layers. This separation is due to the more rapid growth of 

 the exospore. The figures are excellent! — G. F. S.-E. 



Silver-leaf Disease. 



Silver-leaf Disease. By J. Percival (Journ. Linn. Sac, Bot. 

 vol. xxxv. p. 390, pi. 10 and 5 figures ; July 21, 1902).— This disease, 

 which frequently attacks the Plum and the Peach, less often the 

 Apricot, and only occasionally the Sloe, has hitherto been a complete 

 puzzle to all investigators. There is nothing unusual about the leaves of 

 affected trees, except that, instead of their being green, they are of a 

 peculiar ashy-grey colour ; this peculiar colour is due to the presence of 

 certain spaces filled with air between the cells of the epidermis, and not to 

 any alteration of the colouring matter of the leaf. The affected trees may 

 live for many years in this diseased condition, but they bear little or no 

 fruit. When first noticed the disease is found often to only attack some 

 of the branches on one side of the tree, but later the entire tree becomes 

 affected. The author says : " In advanced cases a discoloration of the 

 central parts of the wood is observable when the stems are cut across, and 

 this sometimes extends to the wood of the finer branches, and into the 

 wood of the leaf-petioles. In milder attacks, where the disease is of recent 

 origin, the wood of the stem and branches is not discoloured as far as the 

 naked eye can determine." After careful examination of the roots, it was 

 found that the roots of affected trees when cut across were always dis- 

 coloured in the centre, and that between that portion and the healthier 

 part surrounding it there were always the hyphas of a fungus, which, on 

 being kept in a moist place for some time, grew and produced the sporo- 

 phores of a fungus known as Stercum purpureum. To prove whether this 

 fungus was the cause of the disease or not, some healthy young Plum-trees 

 of various kinds were inoculated with it on one- and two-year old branches 

 early in March, and in the first week in May the leaves on these branches 

 exhibited the characteristic silvery appearance, " thus showing conclusively 

 that this fungus is the cause of the disease." — G. S. S. 



Anatomy of Plants. 



Spergulese, Polycarpeae, Paronychias, Selerantheae, and 

 Pterantheae, Anatomy of (Beih. But. Cent. bd. xii. pp. 139-181, pis. 3 

 and 4). — Herr Friedrich Joesting has written an important paper on this 

 group of plants. The general anatomical characters are as follows : — 



The root is primarily diarch, and the phloem is without hard-bast 

 elements. Development of the periderm begins at an early date. It 

 may be formed from the pericambium, from the inner layers of the 

 cortex, or from the sub-epidermal layer. The cambium, in a great 

 number of genera, ceases at certain points to form wood. Only paren- 

 chyma is developed at these places, hence the wood is divided into many 

 radiating wedges. Secondary cambiums were found in nine of the thirty- 

 three genera investigated. They arise either in the cortex, in the phello- 

 derm, or in the phloem parenchyma. Papillary outgrowths of the 



