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old. The canker may extend at several points along the margin, producing 
a lobed or somewhat concentric appearance. Frequently the canker is 
limited permanently by a crack and the wound is calloused. 
Make prawincs to show the points brought out in 5 and 6. 
On the foliage. Examine the material provided and opsERVE:— 
7. That the spots on the leaves are at first irregular, light- 
brown, vellowish or whitish and small, measuring 1.5 millimeters or less 
in diameter. Their distribution over the surface of the leaf is without 
order. On account of their minuteness, several may appear on a leaf 
without attracting attention, and perhaps without great injury; in more 
severe cases several hundred spots frequently appear on a single leaf. 
Badly diseased leaves may fall prematurely. The leaf-petioles may be 
girdled and instead: of the leaves falling, they may die, turn brown, and 
hang on the tree. 
DRAW to illustrate the symptoms of the disease on leaves, as observed. 
(See Pl. Ind. Bur. Bul. 144, pl. I.) 
ETIOLOGY 
The pathogene causing apple blotch is known as Phyllosticta solitaria 
Ellis and Everhart. This name applies to the asexual stage, no sexual 
stage being known. It may be regarded as an ascomycete, even in the 
absence of a perithecial:- stage, but until the missing stage is found, it is 
temporarily grouped with the Fungi Imperfecti. 
Life-history. A number of important links in the life-history of 
this pathogene remain to be discovered. Enough, however, is known to 
account for its whereabouts throughout the year. 
The Primary Cycles are initiated rather late in the spring, usually 
a month or more after the petals fall. 
Pathogenesis. 'Twig-cankers are the chief sources of the inoculum. 
The fungus hibernates in these lesions as mycelium which becomes active 
in the spring and which produces pycnidia along the advancing margin of 
the canker. Examine the twigs provided. oBSERVE:— 
8. The minute black pycnidia in the bark near the margin of 
the cankers. DRaw to show their appearance under a hand-lens. 
Crush a bit of the bark containing pycnidia and examine for pycno- 
spores. OBSERVE :— 
9. That they are ovoid-elliptical, hyalife, one-celled. DRAW. 
; 10. That they sometimes exhibit a gelatinous sheath, as shown 
in Pl. Ind. Bur. Bul. 144, pl. III, fig. 2-5. copy to show this. These 
pycnospores are washed or carried to the young fruits, twigs and leaves. 
Germination of these pycnospores occurs in twelve to eighteen hours. 
Examine the germinating spores and OBSERVE :-— 
; 11. Number and position of the germtubes; branching, septa- 
tion and contents. DRAW or copy PI. Ind. Bur..Bul. 144, pl. III, fig. 6-7. 
The mycelium developed from the germtubes ramifies the tissues of the 
fruit in a stellate fashion as may be observed by a careful examination 
of the lesions. Pycnidia are soon developed by this mycelium beneath 
asd oe Study prepared slides showing the pycnidia in section. 
ERVE -— 
_ 12. The position and relation of the mature pycnidium to the 
host-tissues. 
