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15. The pycnia; their form and contents. 
. 16. The aecia; their position with reference to the pycnia, the 
relative size of the two structures; their form, structure and contents. 
. Make a DRAWING to show the points observed in 14, 15 and 16. (See 
Virginia Tech. bul. 9, fig. 13.) 
The pycnial stage always precedes the aecial stage in the development 
of those rust-fungi possessing these spore-forms. Aeciospores never re- 
infect the apple. 
Secondary Cycles 
_ Pathogenesis. The inoculum for the secondary cycles consists 
of aeciospores which are discharged from July first to the end of the grow- 
ing-season. They are blown to the red cedar and there initiate-the cedar- 
apples. The aeciospores apparently must undergo a period of rest before 
germination. The question of whether infection occurs in the fall or 
spring is yet unsettled. The way in which the germtube gets into the 
cedar isnot known. The manner of germination is not essentially different 
from that of other fungous spores. A simple germtube is formed; this 
on entrance into the host-tissue develops into a mycelium which stimulates 
the growing cells, and a gall results. This becomes evident the following 
June. Study the young green galls provided. These increase in size’ 
during the. summer and become brown and full sized by winter. The 
fungus passes the second winter of its life-history as mycelium in the full- 
sized gall. From the gall provided, remove a small bit of tissue to a drop 
of water on a slide and crush. OBSERVE :— 
17. The hyphal threads throughout the mount. The character 
of the host-cells. 
Examine prepared sections through mature galls. NOTE:— 
18. That the gall shows cortex and vascular elements. 
19. The mycelium of the fungus and its relation to the host-cells. 
Are haustoria present? 
In early spring the mycelium forms, at certain places beneath the 
cortex, stromata from which are developed the telial horns. Examine 
galls showing these horns. NOTE:— 
20. That the horns arise from galls as described. 
21. The depression at the base of. each horn. 
22. The color, size and shape of the horns. What is their con- 
sistency when dry; when wet? 
On the end of each long stalk-cell (sporophore) a teliospore is devel- 
oped. These are matured by March and April. Germination of the 
teliospore results in the formation of a promycelium which bears sporidia. 
Make a mount of teliospores from the horns provided. OBSERVE :— 
23. The size, shape and color of the teliospores. 
24. Their manner of germination. (See Virginia Tech. bul. 
9, fig. 8, and Nebraska Rept. 22, pl. 3, fig. 5.) 
Make a DRAWING to show the points observed in paragraphs 17 to 24 
inclusive. (See Virginia Tech. bul. 9, fig. 5-8.) 
There is no saprogenesis in either the primary or secondary cycles. 
REPORT 
1. Discuss the relation of apple rust to environment. 
2. Summarize the practical value of such information. 
