1 910-19 1 1.] Notes on Parasitic Ascomycetes. 337 



tagnei Lev., and >S^. mors-uvce Berk. S. pannosa is developed 

 on leaves, &c., of roses, where in its conidial condition (known 

 as Oidium leucoconium Desm.) it gives rise to the rose-mildew 

 common in gardens in autumn. >S'. Castagnei often occurs in 

 its conidial state as mildew on the leaves of hop, as well as on 

 those of meadow-sweet, lady's-mantle, willow-herb, and vari- 

 ous other plants. It is also said to have proved in some 

 seasons very destructive to the strawberry crop in certain 

 localities. 



Mention must also be made of S. mors-uvce, the American 

 gooseberry-mildew, which is a common parasite on the twigs, 

 leaves, and fruit of that shrub in the United States. This 

 destructive species made its first appearance in Europe about 

 eleven years ago, when it was detected in County Antrim, 

 Ireland. Since then it has spread through various parts of 

 England, as well as reached several other countries of Northern 

 Europe. It usually makes its appearance, about the end of 

 May, on the expanding leaf-buds and leaves, and soon passes 

 to the young fruit and twigs, which it covers with a very 

 delicate white film. This gradually becomes more compact 

 and mealy through the growth of upright chains of conidia. 

 At this stage the fungus is liable to be widely spread through 

 the dispersal of its conidia by means of wind, rain, birds, 

 insects, and other agencies. Each conidium is capable of 

 starting a new centre of infection on any growing part of a 

 gooseberry-bush where it may happen to alight. As the 

 season advances the white felted coat of hyphse grows denser 

 in appearance, changes to a dingy-brown colour, and becomes 

 studded over with dark-brown perithecia. Many of the latter 

 fall to the ground, and thus constitute a source of danger 

 during the following season ; but most of the mycelium, with 

 many perithecia attached thereto, adheres to the shoots till 

 next spring. The spores then germinate, produce a new 

 mycelium which passes to the young leaves and fruit, and 

 so repeat the process of infection. Fortunately this destruc- 

 tive pest is as yet known to us only by repute and not by 

 actual experience. 



In the next genus, Phyllactinia, the perithecia are de- 

 pressed, and bear straight appendages, which have a bulbous 

 base and sharp point. Each perithecium contains numerous 



