50 
are the setae, which distinguish the genus Colletotrichum from Gloeo- 
sporium, another anthracnose-producing group of organisms. __ 
Make a diagrammatic DRAWING of a lesion showing the relation of the 
acervuli to the host-tissue. Make an enlarged prRawInc of a portion of an 
acervulus, showing its structure. ; . 
If fresh pods showing the oozing spores are not available examine the 
cultures provided and OBSERVE :— . ; : 
16. The pink masses of spores embedded in a gelatinous matrix. 
It is in this manner that they ooze from the acervulus and are later washed 
or splashed by the rain to initiate new infections. They are formed so fast 
by successive constrictions of the conidiophores that many millions may be 
formed on one badly diseased pod. 
If conditions are favorable, the mycelium in the lesions on the pods 
grows through the tissue and into the seed below it. It is in this manner 
that the bean seed becomes infected with the fungus-hyphae which pro- 
duce spores on the growing cotyledons the following season. 
Cut through a bean-pod directly over a lesion and OBSERVE :— 
17. The depth of the diseased area and the relation which the 
pod-lesion bears to the discolored area on the seed. Make a pRAWING 
showing this relation. 
In this manner the pathogene usually completes the cycle without 
going through a saprogenic period of existence. 
Saprogenesis. The mycelium in the pods and stalks develops 
saprophytically after they are harvested or fall tothe ground. Here are 
produce conidia whenever sufficient moisture and favorable temperature 
allows. If such debris is scattered with manure on land planted to beans, 
conidia produced thereon might cause primary infections in the spring. 
Observation indicates that this rarely occurs and that diseased seed is 
the usual source of the primary inoculum. 
Pathological Histology. Study cross-sections through lesions on 
cotyledons, stems or pods. (If freehand, stain with methyl blue or 
eosin. Wash thoroughly.) oBSERVE:— 
18. The broken-down mass of cells causing a deep depression 
in the tissues, leaving a blackened layer of disintegrating cell-walls at the 
base of the depression. 
; 19. The numerous mycelial threads which are both inter- and 
intracellular, sometimes almost completely filling the cell; the individual 
hyphae which are septate and much branched, and the granular contents 
with numerous bubble-like bodies scattered throughout the threads. 
Are these bodies vacuoles or nuclei? 
20. The effect on the cell-contents, i.e. protoplast, starch or 
chloroplasts. 
Make a DRAWING showing points brought out above. 
REPORT 
: 1. Outline a method of eradication by which clean crops of a sus- 
ceptible variety of beans may be eventually obtained, starting with diseased 
seed ; (a) for a northern grower; (b) for a grower in the Gulf states or the 
southwest. 
