SPHAEROTHECA 151 



important that the spring wave of disease, which is apt to be 

 neglected on account of the small quantity present, be 

 thoroughly stamped out, otherwise it lingers in small quantity, 

 and starts the more serious summer wave of disease. 



Massee, The Enemies of the Rose, National Rose Soc. 

 (1908). 



Strawberry mildew. This disease, caused by Sphaerotheca 

 humuli (Burr.), has long been known as destructive to straw- 

 berries. Berkeley records an instance of a crop of straw- 

 berries having been completely destroyed by this fungus in 

 1854. Both foliage and fruit are attacked, but in many 

 instances the leaves alone suffer ; there are no conspicuous 

 blotches or spots present on the upper surface of the leaves, 

 but the certain indication of the presence of the parasite is 

 the gradual turning upwards of the edge of the leaf, until 

 nearly the whole of the under surface is exposed, which, if 

 examined with a pocket-lens, is seen to be covered with a 

 delicate whitish down the conidial condition of the fungus. 

 This often occurs rather late in the season, after the fruit has 

 been gathered, when almost every leaf in a field presents the 

 strongly turned up appearance. The greatest amount of 

 damage is done when the leaves are attacked early in the 

 season, during the flowering stage, as not infrequently the 

 fungus passes on to the ripening fruit, which is totally 

 destroyed. I have seen a heavy crop of fruit so completely 

 covered with the conidial form of the fungus, that the berries 

 presented the appearance of having been thickly dredged with 

 flour. I once saw large quantities of strawberries presenting 

 a very dull, water-logged appearance exposed for sale in the 

 market at Yarmouth, and on investigating the matter, learned 

 that the fruit was covered with white powder, the fungus under 

 consideration, which had been more or less removed by shak- 

 ing the fruit in water. The experiment was not a success, as 

 what little sweetness and flavour was left by the fungus had 

 been removed by the water. The perithecia or winter-fruit, 

 which alone are responsible for the appearance of the fungus 

 each season, has not, so far as I am aware, been met with on 

 the strawberry in this country, although they have been 

 reported from the United States, where the fungus is equally 

 common and destructive as with us. Notwithstanding the 

 absence of winter-fruit on strawberry plants, when it is remem- 



