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spreading mycelium. From the mycelium, within less than a month, 
are produced first pycnia and promptly after them, aecia. 
Study cross-sections of the leaf (freehand or prepared) through an 
aecial lesion. OBSERVE :— 
15. The large cup-like aecia and opposite them on the upper 
surface of the leaf, the minute flask-shaped pycnia (spermagonia). 
Locate a pycnium and study its structure under high-power. MAKE 
ouUT:— 
16. The very slender interwoven mycelium forming the pycnial 
wall. 
17. The long slender sporophores arising from the wall-mycelium 
and converging at the center of the pycnium about a small cavity which 
is filled with very minute bacterium-like pycnospores (spermatia). 
18. The protruding neck of the ostiolum through which the 
spermatia are discharged. These spermatia have now no known function. 
They will not germinate and are supposed to be vestigial male cells (sperms). 
Study an aecium and OBSERVE :— 
19. That it is sunken in the tissues; at first covered by the 
epidermis of the host (see one that has not burst through). The pycnia 
are more superficial; subepidermal or subcuticular? 
20. The fine interwoven mycelial threads between the host- 
cells about the aecia. Do they ever penetrate into the host-cells? 
21. That it is from a densely interwoven mat of this mycelium 
(to be seen at the base) that the structures of the aecium are developed. 
22. The closely packed club-shaped sporophores arising from 
the mycelial mat in the base of the cup. 
23. The chains of spores cut off from each sporophore, forming 
the parenchyma-like mass that fills the cup. Why are the aeciospores 
here angular in outline? Note that the maturing spores at the mouth of 
the aecium become globose. 
24. The large cells lining the cup,—peridial cells. They also 
arise in chains from short mycelial branches similar to sporophores. Note 
the difference in thickness of the wall of the inner and outer faces of the 
cells. This lining of the cup is pséudoparenchymatous and is called the 
peridium. 
The mycelium of the aecial stage arises from the uninucleate sporidium 
and each mycelial cell is uninucleate. When the formation of the aecium 
begins, there is a sexual fusion of many pairs of mycelial tips in the region 
where the base of the cup is to be. From each pair of branches arises 
a single binucleate stalk,—a sporophore of the aecium. A chain of spores 
is developed from each of these binucleate sporophores by successive 
conjugate divisions of the paired nuclei and the laying-down of a septum 
between the resulting pairs thus formed. Examine stained sections 
carefully under high-power and LOocaTE :— 
25. The paired nuclei in the sporophores; ‘in the aeciospores. 
Make a DRAWING to show the structure of the aecium, pycnium and 
their relation to the host-tissue as seen in section. 
Remove with the needle or scalpel some mature aeciospores from the 
cups on diseased leaves provided. If dry, mount in potassium hydroxide. 
Study and oBsERVE:— , 
26. Their form, size, color and contents; markings on the 
epispore. DRAW several aeciospores. 
