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12. The water-soaked zone in the tissue about the soft mycelium- 
coated center of the lesion. 
DRAW to show the external appearance of rotted roots. 
Cut the root lengthwise through the lesion. oBSERVE:— 
13. The depth to which the lesion extends. What tissues of the 
root are involved? 
DRAW to show internal characters of the rot in the roots. 
ETIOLOGY 
The disease is caused by the ascomycete, Sclerotinia Libertiana Fuckel 
(= Sclerotinia sclerotiorum (Libert) de Bary). 
Life-history. 
Primary Cycle. 
Pathogenesis. The source of inoculum for the primary cycle is 
the apothecium developed in the spring from the overwintered sclerotium. 
Examine the specimen provided. oBSERVE:— 
14. The large black sclerotium and the trumpet-shaped apothe- 
cium with stalk and concave disk. praw. From this apothecium are 
shot forth the ascospores which constitute the inoculum of the primary 
cycle. 
The character of this inoculum may be determined as follows: Gently 
break the seal and remove the cover from the glass preparation-dish 
in which are living apothecia. Watching sharply, OBSERVE :— 
15. The tiny cloud of spores that puff from the disc of the apothe- 
cium. This cloud is composed of ascospores which caught by the breeze 
are borne about and lodging in a suitable infection-court initiate the cycle. 
All of the ascospores of an apothecium are not discharged at one time. 
With your forceps carefully remove a bit from the edge of the apothe- 
cium and crushin a drop of wateron a slide. Cover and study. oBSERVE:— 
16. The ascospores; their form, number in each ascus, and color. 
DRAW to show several ascospores much enlarged. 
Once within the infection-court where sufficient moisture is available, 
these germinate forming a germtube which soon branches to form mycelium 
and finally penetrates into the host-tissues. Examine the germinating 
ascospores provided. OBSERVE :— 
17. From what place on the spore the germtube arises; relative 
size of spore and germtube, branching, contents. Draw. This germ- 
tube branches forming the mycelium which spreads through the tissues, 
causing the rot. 
Remove a bit of the rotten tissue and tease apart in a drop of water on 
a slide. Cover and examine for mycelium. OBSERVE:— 
18. Size, septation, branching, color, relation to host-cells, 
(inter- or intracellular’). Do haustoria occur? 
As this pathogene grows readily in culture, the mycelium may be 
advantageously studied in the agar-culturé in the petri-dish provided. 
Carefully cut out a small square from the advancing margin of the colony, 
transfer to a slide in a drop of water, cover and with little or no crushing, 
study the mycelium, comparing this with that found in the tissues. 
DRAw to show the characters of the mycelium of S. Libertiana. 
Saprogenesis. No conidia are probably ever produced by this 
fungus during its normal life-cycles; certainly not during pathogenesis. 
