PLANT DISEASES. . 87 



her eggs. A thorough investigation of the responses made by 

 insects to volatile chemical substances is likely, therefore, to 

 yield important results, possibly in the direction of leading to 

 methods of controlling such pests as the pear midge and the 

 apple blossom weevil, which have hitherto resisted all attempts 

 to control their ravages. The method is, of course, widely used 

 in some directions, as, for example, in hospitals, for the control 

 of house flies; in America, by the use of poisoned sprays to 

 attract certain pests; in Australia, as a method of controlling 

 fly pests of sheep. The subject is now being investigated at 

 Rothamsted, the work up to the present being largely the testing 

 of a number of volatile substances with a view to determining 

 their attractive properties. These substances do not necessarily 

 occur in the immediate environment of the insect, for it is known 

 that certain insects are attracted towards chemical substances 

 that are neither associated with the smell of the food nor occur 

 in their immediate neighbourhood. A large number of sub- 

 stances have been tested and it has been found that : — (i) beer, 

 cane molasses, • and mixtures of these substances, are very 

 attractive; (2) alcohols are not markedly attractive, with the 

 exception of normal propyl-alcohol ; (3) acids, mineral and 

 organic, are not markedly attractive; (4) alcohols mixed with 

 certain acids are highly attractive. The work is being continued. 



Agricultural and Horticultural Research Station, 

 Long Ashton, Bristol. 

 " Big Bud " and Reversion of Black Currants. — " Big Bud " 

 of black currants has been known for at least 70 years; " Rever- 

 sion " for at least 20. The two diseases are prevalent wherever 

 black currants are grown, and cause especially serious losses in 

 the Eastern counties. Bad cases of " reversion " wiU reduce the 

 crop to 5 cwt. per acre or less, as compared with an average crop 

 of about a ton. A noticeable feature of the diseases is the 

 frequency with which one accompanies the other. In the case 

 of " big bud," the damage is caused by a mite which enters the 

 growing point of the shoot, where it rapidly multiplies causing 

 sweUing of the bud scales and destruction of the flower embryo. 

 In " reversion," the leaves are longer in proportion to their 

 breadth; the leaf margins are more coarsely serrated; the leaf 

 veins decrease in number; there is an extensive growth of 

 lateral buds resulting in a crowded instead of an open form of 

 bush ; and the fruit falls off before it attains fuU size. Work on 

 " reversion " has been in progress at Long Ashton for six years. 

 An important initial difficulty arose from the fact that there 



