49 
8. The numerous small hyaline conidia mixed with the debris 
of diseased tissues. Their shape, sizeand color. pRraw. These constitute . 
the primary inoculum. They are washed or splashed by rain to the 
stalks and first leaves of the seedling which thus inoculated show within a 
few days the lesions of the primary infection. The cotyledons soon 
shrivel and fall carrying with them the source of primary inoculum. If 
dry weather prevails from the time the beans come up until the cotyledons 
fall, few or no primary infections occur and a clean crop is assured. 
The conidia, washed from the cotyledon-lesions, germinate on the stems 
or leaves by a germtube. This penetrates directly into the tissues or 
forms a resting-cell at its tip,—an appressorium, from which later a germ- 
tube penetrates the cell on which it rests. Study germinating conidia 
provided and OBSERVE :—- 
9. The number and positional origin of the germtubes. Note 
that the identity of the conidium is nearly or quite lost in the developing 
mycelium. 
10. The darker thick-walled appressoria at the ends of some of 
the germtubes. What is their function? 
DRAW germinating conidia. 
There are soon developed in the primary lesions on the seedling-leaves 
and stems, minute fruit-bodies. Examine the lesions and OBSERVE :— 
11. The number and location of these fruit-bodies,—the acervuli. 
Color? Some of them may show (if fresh specimens) the pink mass of 
conidia oozing out on the surface of the lesion. DRAw to show the appear- 
ance of these acervuli in the lesion as seen under the hand-lens. 
Mount and examine some of the conidia from a primary lesion to see 
that they are the same as those from the cotyledons. Conidia from the 
primary lesions are produced for a considerable period and initiate the 
secondary cycles. 
Saprogenesis. The mycelium in the old primary lesions may con- 
tinue to live and spread saprophytically into the dead tissues of the leaves 
and stems, on which in the spring it may produce conidia. These conidia 
probably seldom function in initiating primary infections. The sexual 
stage may develop from the saprophytic mycelium in old stems and 
leaves but is not certainly known for this pathogene. 
Secondary Cycles develop on the later leaves and onthe pods. The 
same phenomena of inoculation and infection are exhibited as in the 
primary cycle. 
Pathogenesis. The lesions on pods afford the best material for a 
study of the structure of the fruit-bodies of the pathogene. 
Study cross-sections through a lesion. OBSERVE :— 
12. The saucer-shaped acervuli, at the surface of the lesion; 
their relation to the host-tissues, especially the epidermis. 
13. The thin mat of mycelium forming the base of the acervulus, 
from which arise the conidiophores. 
14. The size and shape of the spores; the manner in which they 
are attached to the conidiophores. What are the bubble-like bodies 
found embedded in the granular contents of each? Do the spores have 
septa? 
15. The dark tapering septate threads which extend above 
the conidiophores and have somewhat the appearance of spines. These 
