IGNIARIUS HEART-ROT 
This is the most common of the numerous heart-rot diseases of decidu- 
ous trees and may be taken as a type. The fungi causing heart-rots of 
deciduous trees are more or less alike in their life-habits and the methods 
for their control are similar. (In this connection, see von Schrenk and 
Spaulding, Diseases of Deciduous Forest Trees. Pl. Ind. Bur. Bul. 149: 
1-85, pl. 1-10, fig. I-X, and extensive bibliography.) 
SYMPTOMS 
External signs. In the material provided, oBSERVE :— 
1. That the only external evidence of the disease is the bracket- 
like sporophore of the fungus. ; 
2. The point at which the sporophore emerges. Why? (See 
Pl. Ind. Bur. Bul. 149, pl. I.) 
3. The variation in the size of the sporophores. Upon what two 
factors does this variation depend? 
4. The age of different sporophores. 
5. The characteristics, shape and color of the sporophores. Com- 
pare with other specimens on the demonstration table. 
Make a DRAWING to show characteristics of the sporophore in position 
on the host. 
Internal symptoms. In the transverse and longitudinally sawed 
sections of diseased wood provided, OBSERVE :— 
6. The rotted wood at the center of the lesion; white or yellow- 
ish white and more or less soft and crumbly. © 
7. The distinct black line or lines bounding the white rotted 
areas. 
8. The light-brown or yellowish brown zone of firm hard wood 
just outside the outermost black line. Cause of the discoloration? 
9. The brown felty character of the mycelial growth from the 
cut ends of the sticks. 
Make prawincs to show the symptoms as seen in the transverse and 
longitudinal sections. 
ETIOLOGY 
This disease is caused by a basidiomycetous fungus, Fomes igniartus 
(Linneus) Fries, one of the perennial species of the family Polyporaceae. 
Life-history. This fungus, although largely confined in its activities 
to the heart-wood of its host, may be regarded as a true pathogene, be- 
cause it develops only in living trees. 
Primary Cycles only are known, the infections occurring once a year. 
With our present limited knowledge of this fungus, no sharp line can be 
drawn, if any exists, between its saprogenic and pathogenic activities. 
The source of inoculum is the compound sporophore on the living tree. 
Study several of the sporophores provided and OBSERVE :— 
10. The cracked and checked, hard black upper surface of the 
sporophores. , ; 
11. The uprolled reddish brown margin of the last-formed annual 
pore-layer. 
12. The brown surface of the pore-layer. 
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