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But one crop of aeciospores is produced. With the maturity and 
discharge of the last aeciospores, the activities of the primary cycles cease. 
The aeciospores initiate secondary cycles on the cereal-hosts through which 
the pathogene perpetuates itself until the following year. There is no 
saprogenesis in the primary cycles. 
Secondary Cycles, especially the late ones, develop chiefly on the 
leaf-sheaths and stems of the wheat, oats or grass-hosts. Leaves may 
also become infected. 
Pathogenesis. The first secondary cycles are initiated by aecio- 
spores which, falling upon the host, germinate in the dew or raindrops 
sending out a germtube which rapidly grows along over the surface until 
its tip reaches a stoma through which it penetrates to the tissues within. 
The protoplasm of the spore passes out into the germtube keeping con- 
stantly in its tip as it grows. Within the substomatal cavity, the tip of the 
germtube applies itself to one of the parenchymal cells and sends into it a 
short blunt branch,—a haustorium. 
Having thus established a food-relation with the host, a binucleate 
ramifying mycelium is developed. This mycelium produces mature. 
uredinia within two or three weeks. 
Study cross-sections (freehand or prepared) of a stem through a uredi- 
nium and MAKE OUT:— 
27. The structure of the sorus and its relation to the host-tissué. 
28. The intercellular mycelium. Can the globose haustoria be 
found? 
29. The stout sporophores arising from the mycelium, each 
bearing at its apex a uredospore in some stage of development, or mature. 
How can one tell whether the spore is young or mature? 
Make a DRAWING of a cross-section through the uredinium. 
Scrape some uredospores from a diseased stalk; mount in potassium 
hydroxide and OBSERVE :— 
30. The form, size, color and contents of the uredospore as 
compared with the aeciospores; markings on the epispore, if any. 
These uredospores are usually wind-disseminated, initiating other 
secondary cycles. They germinate at once in moisture, even in a moist 
atmosphere. They infect the host in a manner and under conditions 
similar to the aeciospores. The germtubes emerge through special pores 
or thin places in the spore-wall. Mount and examine uredospores that 
have been treated with acetic acid. OBSERVE :— 
31. The size, number and location of the pores. DRAW. 
For germination and penetration into the host, study illustrations 
provided. Supplement this with a study of germinating spores on slides, 
if available. Make prawIncs to show the points brought out. 
From the mycelium produced from the uredospore, other uredinia 
with mature uredospores are produced. This may be repeated seven or 
eight times during the growing-season. The mycelium remains binu- 
cleate throughout all the uredospore-generations, the spores being binu- 
cleate also. 
As the host begins to mature, there is developed from the mycelium 
in the secondary lesions, not uredospores but another spore-form,— 
chlamydospores, black resting-spores known as teliospores (teleutospores). 
They often arise at first in the same sorus with the uredospores, later they 
