71 
To study the structure and arrangement of these subcuticular strands, 
use prepared stained surface-mounts or make such mounts under direction 
of the instructor. Some mycelial threads penetrate throughout the leaf- 
tissue beneath. At certain places on the subcuticular mycelium, the 
conidial fruit-bodies are developed. 
Again examining one of the old dark spots with the hand-lens, MAKE 
OUT :-— 
8. The conidial fruit-bodies, minute black specks,—the acervuli. 
Make an enlarged diagrammatic DRAWING to show surface view of the 
subcuticular mycelium and acervuli in their proper relation to each other 
and to the leaf. 
Make thin cross-sections through a spot showing numerous acervuli. 
Stain with methylene blue, wash, cover and OBSERVE :— 
9. The relation of the acervuli to the leaf-tissues; subepidermal, 
subcuticular, or on the surface? (Compare with prepared stained slides.) 
10. Structure of acervulus, conidiophores and conidia. 
11. Mycelium, in epidermal cells and palisade-tissues, beneath 
the acervulus; inter- or intracellular? 
Make a detailed prawinc of a section through the acervulus. 
These conidia, either borne by the wind or splashed by rain to healthy 
leaves, germinate to initiate the secondary cycles. Study germinating 
conidia and pRaw; or copy Bot. Gaz. 54, pl. XIII, fig. 3. 
Saprogenesis. After the diseased leaves fall to the ground, the 
subcuticular mycelium forms peculiar shield-like structures, beneath 
which in the leaf-tissue below the epidermal cells, the mycelium forms a 
perithecium. These perithecia begin to form in the autumn but do not 
mature until spring. 
If prepared sections are available, study and work out ini a DRAWING, 
the structure of the perithecium, or copy figures from Wolf’s article in 
Bot. Gaz. 54, pl. XIII. 
Secondary Cycles. These are initiated repeatedly throughout the 
season by conidia from acervuli. Leaves involved in the secondary 
cycles fall prematurely like those suffering from the primary infections 
and the next spring also produce a crop of ascospores. 
Pathological Histology. The brown or black coloration of the spots 
is due to the necrosis of the epidermal and palisade-cells and not to the 
mycelium as one might expect. 
12. If fresh leaves are available, make thin cross-sections 
through a spot and verify the above statement. 
SKETCH in detail a few diseased and healthy cells to show effects on the 
protoplasm and cell-organs. 
REPORT 
1. Detail in a letter to a grower of outdoor-roses two methods 
for the control of this disease, one an eradication-method, the other a pro- 
tection-method and show how one may be made to supplement and streng- 
then the other. Assume that the grower knows the facts of the life- 
history of the pathogene. 
