PODOSPHAERA 145 



Mycelium white at first, in some species becoming brown 

 with age. Spores hyaline, continuous. Erysipheae. 



Mycelium black. Spores coloured or hyaline, continuous 

 or variously septate. Perisporieae. 



Salmon, E. S., ' A Monograph of the Erysiphaceae,' Mem. 

 Torrey Bot. Club. New York. 



PODOSPHAERA (K.UNZE) 



Perithecia with the appendages springing from the apex, 

 or the equatorial region, tips of appendages forked, ascus 

 solitary, 8-spored. 



Distinguished from Sphaerotheca, the only other genus 

 having only one ascus in the perithecium, by the appen- 

 dages not originating from the base of the ascus. 



Powdery mildew of the cherry (Podosphaera oxyacanthae, 

 De Bary) often proves very injurious not only to the foliage 

 of the cherry, but also to that of the apple, peach, quince, 

 and various other cultivated and wild plants belonging to 

 Rosaceae. It first appears under the form of small, scattered, 

 whitish patches on both surfaces of the leaf, these patches 

 gradually extend until the greater part, or the whole, of the 

 leaf is covered. It also attacks the young shoots. As a 

 rule perithecia are sparingly produced, and on some hosts 

 where the conidial form is abundant, the winter fruit has 

 never been observed. It is suspected that the mycelium 

 hibernates during the winter on the host. 



Mycelium persistent or almost disappearing, perithecia 

 subglobose, appendages very variable in number and in 

 length, springing from the equator or nearer the apex of the 

 perithecium, basal portion brown, apex 2-4 times forked, 

 ultimate branchlets more or less knobbed, ascus pear-shaped, 

 containing 6-8 spores of variable size, i6-3oX 10-20 p.. 



But little injury results when full-grown foliage is attacked, 

 but when the leaves are young, and tender shoots are in- 

 fected, the damage is often very serious, and nursery stock 

 more, especially is often killed outright. Bordeaux mixture, 

 commencing with half-strength solution when .the leaves are 

 young and soft, will arrest the course of the disease. 



Waite, M. B., Ann. Rep. Dept. Agric. U.S. (1888). 



K 



