30 
Make prawincs showing the structure of the sexual bodies and fertili- 
zation of the oosphere. ; . " 
The fertilized oospores now go into a resting-period and will not germi- 
nate at once. Normally this dormant period extends through the winter. 
During the spring, changes in the oily protoplasm of the oospore take place 
which make its germination possible. With germination of these oospores 
(already studied) the primary cycle is completed. : 
Secondary Cycles are initiated repeatedly during the growing-season 
as has already been pointed out, either by conidia or by mycelium spread- 
ing thtough the soil. If viable conidia are available study conidial germina- 
tion on the slides provided; or Cornell Bul. 363, fig. 16-17; and read Pp. 97-99. 
Make prawincs illustrating ways in which conidia (sporangia) -getmi- 
nate; also the structure and germination of the swarmspores. How do 
the germtubes gain entrance to the host-tissues? Why can they not 
penetrate mature tissues? 
The further developments of the pathogene during the secondary 
cycles duplicate those of the primary. 
Pathological Histology. The pathologic effects of these pathogenes 
are of the simplest sort—a direct killing of the protoplasts—necrosis. 
Study sections through the advancing margin of the lesion, using fresh 
material. OBSERVE :— 
16. The plasmolyzed and disorganized cell-contents. 
_ 17. The watér-soaked appearance of the.diseased tissues due to 
the diffusion of the cell-sap into the intercellular spaces, forcing out the 
air. 
DRAW to show these effects. 
Pathogenicity Studies. The rapid destructiveness of these pathogenes 
in a bed or flat of closely crowded seedlings is strikingly brought out by a 
Simple inoculation experiment. 
Under the direction of the instructor each student will inoculate 
the seedlings provided, with pure cultures of one or the other of these 
fungi. Keep under moist conditions and examine daily for first evidencés 
of infection and successive symptoms. Make notes on conditions under 
which the inoculated plants were kept, length of incubation-period, 
effects of removing plants to dry conditions before all go down and other 
facts observed. 
REPORT 
1. Describe in detail and explain the functions of the structures 
developed by either of these pathogenes during its life-cycles. 
5 2. Prepare a complete report on the pathogenicity-studies 
made. 
