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These swarmspores swim about in the water on the leaves for a short 
time, then round up, secrete a wall about themselves and send forth a germ- 
tube which penetrates the leaf and develops a mycelium within the tissues. 
The germtube may enter through a stoma or bore directly through the 
walls of the epidermal cells. copy the figures of swarmspore-germination 
and penetration from Connecticut Ann. rept. 1904, pl. XX XI. 
The mycelium in the leaf is difficult to study, and as it is of the same 
character as that of the pathogene of grape mildew, the grape stem will be 
used instead. Cut a thin longitudinal section of the stem provided, 
stain slightly with eosin and OBSERVE :— 
7. The granular mycelial threads between the cells. The my- 
celium is cenocytic. 
8. The button-like haustoria which branch from these threads 
and push through the cell-walls of the host. 
Make a DRAWING illustrating the mycelium with some of the host-cells 
and the haustoria pressing through the walls. 
The mycelium rapidly kills the tissues and as it does so it sends forth 
through the stomata on the under surface of the lesion long branched 
fruiting stalks,—the conidiophores. 
Scrape with a scalpel several spots on the under side of the leaf and 
place the substance on a slide in a drop of water. With the high-power, 
OBSERVE -— 
9. The long sparingly branched conidiophores with slightly 
swollen base, and the beak-shaped tips at the ends of the branches,-to which 
are attached the conidia. . 
Make an enlarged pRAwING of a conidiophore, showing conidia at- 
tached. 
These conidia are disseminated by the wind and initiate new secondary 
cycles. 
This pathogene sometimes attacks the wild cucumber, Echinocystis 
lobata (Michx.) T & G., but there is on this host another downy mildew 
pathogene, Plasmopara australis (Spegazzini) Swingle. To show the 
difference between these two pathogenes examine diseased leaves of 
E. lobata provided and OBSERVE :— 
10. The downy white spots on the lower side of the cucumber- 
leaf. 
Make a DRAWING of a leaf showing one of these spots. 
Place some of the fungus on a slide and with the high-power, OBSERVE :— 
11. The short conidiophores branched at nght angles: the blunt 
tips with short sterigmata; and the smaller almost globose conidia. 
Make a DRAWING showing the points observed. 
REPORT 
1. Discuss fully the control of the downy mildew of cucurbits. 
