127 
Saprogenesis. The perithecia do not complete their development 
until the late autumn, usually after the leaves fall. Some do not mature 
until the following spring. They develop and mature at the expense 
of food gathered by the parasitic mycelium. Select from the material 
provided, representatives of two or more genera. Study the perithecia. 
OBSERVE :— 
31. The shape, color and structure of the perithecitum; the 
nature of the appendages. DRAW one perithecium with its appendages. 
Study species from the three remaining genera, OUTLINE the perithecia, 
but pRaw carefully a typical appendage for each. (See Salmon, Mono- 
graph of the Ervysiphaceae, pl. 1-7; also Burrill, Parasitic Fungi of 
Mlinois, p. 395-397.) Crush the perithecium in each case and examine. 
In this connection the following key -—- 
A. Perithecia with one ascus. 
1. Appendages simple, undivided at tip........... SPHAEROTHECA 
2. Appendages once or more dichotomously divided at the tip...... 
Satake bape Mts aw 2 wpa 4 ERE SARA OGRE Res PODOSPHAERA 
B. Perithecia with several asci. 
1. Appendages never more than slightly swollen at the base. 
a. Appendages simple, or irregularly branched: without tip 
pecnhanttes: nc kecehite Siduies quienes eaaaeilan ERYSIPHE 
b. Appendages- once or more dichotomously branched at the 
TP o26e-aelguor ts eee ai sy eR ees SoReal MICROSPHAERA 
c. Appendages spirally rolled at the tip.. ........UNCINULA 
2. Appendages swollen at the base so as to form an enlarged plate. . 
sey Aaa ah inns eS dancer a ifort dracuae eae Ns PHYLLACTINIA 
With ascospore-discharge in the spring and early summer, saprogenesis 
of the primary cycle ends. 
The Secondary Cycles are, as pointed out above, initiated by the 
conidia from the primary lesions. They normally repeat in all details 
the phenomena and structures exhibited in primary cycles. Secondary 
cycles may repeatedly initiate other secondary cycles during the season. 
REPORT 
1. Discuss control of one of the powdery mildews which may 
be selected, treating the subject under the headings of eradication and 
protection and explain how the life-habits of the pathogene make effective 
the measures described. 
