146 
over the surface until its tip reaches a stoma through which it penetrates 
to the tissue within. The protoplasm of the spore passes out into the germ- 
tube keeping constantly 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, it grows and develops a ramifying 
binucleate mycelium. This mycelium spreads only locally and produces 
within two or three weeks mature uredinia. Scrape some uredospores from 
a diseased stalk, mount in potassium hydroxide and OBSERVE :— 
24. The form, size, color and contents of the uredospores as 
compared with the aeciospores; markings on the epispore if any. DRAW 
several aeciospores. 
Study cross-sections (freehand or prepared) of a stem through a ured- 
initum and MAKE OUT:— 
25. The structure of the sorus and its relation to the host-tissue. 
26. The intercellular mycelium. Are haustoria formed? (See 
California Bul. 165, fig. 16.) ; 
27. The stout sporophores arising from the mycelium, each bear- 
ing 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 part of the cross-section through the uredinium. 
These uredospores are usually wind-disseminated and initiate other 
secondary cycles. They germinate at once in moisture, even in a moist 
atmosphere. They infect the host in a manner and under conditions simi- 
lar 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 -—: 
28. The size, number and location of the pores. DRaw. For 
germination and penetration into the host, study California Bul. 165, 
fig. 21-22. Supplement with 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 may be produced in twelve days under favorable 
conditions. This is repeated over and over throughout the growing-season. 
The mycelium remains binucleate throughout all the uredospore- 
generations, the spores being binucleate also. 
As the host begins to mature, there is developed from the mycelium 
in the secondary lesions, not uredospores but another spore-form,— 
chlarnydospores, black resting-spores known as teliospores (teleutospores). 
They often arise at first in the same sorus with the uredospores, later they 
appear in sori in which no uredospores are formed. Mount some telio- 
spores in potassium hydroxide and stupy:— 
29. Their form, size and structure as compared with the uredo- 
spores; color, where located, in walls or contents? 
30. The thick walls and densely granular oily contents. 
31. The light spot in the center of each cell; not always evident. 
The nuclei are located here. These spores are at first binucleate but at, or 
just before the germination the nuclei fuse and sexual fertilization, begun 
by the association of nuclei in the aecium, is now completed. 2 
__The structure of the telium and its relation to the host-tissues does not 
differ materially from that of the uredinium. pRaw several teliospores 
to show structures and variations in form and size observed. 
