133 
The Primary Cycles are initiated in early summer at the time the rye 
or other grass-hosts begin to head-out. 
_ Pathogenesis. Ascospores which are produced in the spring 
constitute the inoculum for the primary cycles. From the ergots (sclerotia), 
which overwinter on the ground, there develop in the spring, stalked 
fruit-bodies. In the heads of these are developed numerous perithecia 
containing the asci with long slender ascospores. Examine the specimens 
provided or photograph 4, fig. 22. oBsERVE:— 
7. The little pimple-like dots scattered thickly over the globose 
head of the fruit-body,—the ostiola or mouths of the perithecia. 
From these ostiola the long thread-like ascospores are shot into the air 
and, carried by air-currents, lodge in the infection-courts,—the open blos- 
soms of the rye or other grasses. 
A bit of material from a mature stroma will be provided (take clean 
slide to materials room). Crush, cover and study. OBSERVE:— 
8. The long slender ascospores; some floating free, others still 
in the asci; continuous or septate? DRAw several ascospores. (Keep this 
slide for No. 20.) 
These germinate within the blossom. Examine photograph or de Bary, 
Morphology and Biology of the Fungi, p. 227, for germinating ascospores. 
NOTE -— 
9. That upon germination the spore at once becomes, to all 
intents, a part of the mycelium. copy. 
The branching germtubes quickly penetrate the young ovary and, grow- 
ing throughout its tissues, develop the Sphacelia or conidial form of the 
fungus. 
Study cross-sections (freehand or prepared) of the upper end of the 
ovary (made during the Sphacelia stage). Examine with the high-power. 
OBSERVE :— 
10. The numerous irregular cavities lined with erect conidio- 
phores. Note the irregular dark masses of host-cells. 
DRAW a small portion of the hymenium with underlying host-tissue, 
showing the conidia and the manner in which they are borne. 
The honeydew consists of a sweet fluid, exuded by the pathogene, 
in which great numbers of these conidia find their way to the surface of 
the spikelet. Insects attracted by the honeydew serve as inoculating agents 
in starting the secondary cycles. 
Very soon after, the conidia mature and the mycelium in the basal 
portion of the ovary begins to develop the sclerotium, which, as it grows 
and develops, replaces the host-cells and pushes forth as a long black spur 
with the shriveled Sphacelia structures at its tip. It is at first light 
colored, inclined to purplish but soon turns black. (See illustration 
specimen.) 
Examine photographs 3, fig. 25 and 4, fig. 13-14. NOTE:— _ 
11. That while the sclerotium usually replaces the entire ovary, 
this is not always the case. copy from the above figures to show this. 
Make very thin cross-sections of one of the mature sclerotia and study 
under the high-power. OBSERVE :— 
12. The pseudoparenchymatous structures. : 
13. The thick walls and small lumina of the hyphae composing 
the sclerotium. Are there any evidences of host-tissue? 
