111 
, 15. The large granular mycelium, fitting so closely into the 
intercellular spaces that its walls are not readily distinguished from those 
of its host-cells; septate or non-septate? 
16. The numerous small globose haustoria extending through the 
walls of the host-cells. They push the plasma-membrane inward but do 
not penetrate it. 
Make a DRAWING of the mycelium showing its structure and relation 
to the host-cells. 
This mycelium soon develops special branches which are sent forth 
through the stomata and branching, form the conidiophores. These 
conidiophores constitute the downy white growth on the under surface 
of the lesion. Scrape some of the conidiophores from the specimen pro- 
vided for this purpose. Mount in potassium hydroxide. Examine and 
OBSERVE :-— 
17. Their color, form of branching and shape of the ultimate 
tips or branchlets on which the conidia (sporangia) are borne. Estimate 
carefully the number of conidia that may be borne on each conidiophore. 
18. The egg-shaped conidia lying all about in the mount. 
They separate from the conidiophore very readily when mature. By 
which end were they attached? A mount from near the margin of a 
young lesion may show the immature conidia still attached to the conidio- 
phores. 
Study sections through a leaf-lesion. OBSERVE :— 
19. The relation of the conidiophores to the host-structures; 
emergence through the stomata; number from each stoma; and constric- 
tion at the stomatal opening. : 
Make a large DRawING of a conidiophore with mature conidia attached 
to a few of the branches. 
These conidia are disseminated by the wind. They fall upon leaves, 
fruits and stems and initiate secondary cycles. 
Saprogenesis. The mycelium within the dying leaf-tissue begins 
the sexual formation of long-lived resting-spores to carry the pathogene 
through the winter. 
The early stages in the development of these oospores are not easily 
studied in the case of Plasmopara Viticola, but may be readily observed 
in pure cultures of related phycomycetous fungi. Make mounts from the 
culture provided and OBSERVE -— 
20. The large densely granular swollen tips of many of the my- 
celial branches,—oogonia or female organs. The cross-wall cutting off 
some of the older ones from the mycelium. 
21. The much smaller granular body, also a modified mycelial 
tip, applied closely to the side of the oogonium,—the antheridium or male 
organ. From this.a fertilization-tube is sent into the oogonium and a 
nucleus passes through to fuse with a female nucleus in the oogonium. 
The contents of the fertilized oogonium now round up to form a single 
DRAW to show the early stages in oospore-formation. ; Sy 
Oospore-formation may probably begin while the mycelium is still 
drawing nutriment from the living host-tissues. The oospores are, 
however, not matured until after the tissues in which they are formed 
are dead. The oospores mature in the fallen leaves on the ground. Study 
the mature oospores provided. OBSERVE:— 
