lyigj STKVEyS c- DALBEY—TREE FEKX PARASITE 225 



and top. Asci 51 X 1 7-24 n, ovate. Spores 10 X 17 m> oval, hyaline, 

 I -celled. 



Conidial stage: Pycnidia dimidiate, opening by a ragged cleft, 

 amphigenous but more frequently epiphyllous, circular, 200-315 /u 

 in diameter, 10-30 fx high, black, dimidii^te, closely reticulate, 

 reticulations about 7 m in diameter, occupying the- approximate 

 center of a diseased spot. Spots irregular in outline, 1-3 mm. in 

 diameter, very numerous, spores i-celled, oval or pyriform, dark, 

 obtuse, 28-34X14 M- 



University of Illinois 

 Urbana, 111, 



EXPLANATION OF PLATES XV, X\T 



PLATE XV 



Fig. I. — -Pinnule showing distribution of disease spots. 



Fig. 2. — Frond segment with spots. 



Fig. 3. — Top views of pycnidia with openings. 



Fig. 4. — Detail of dermal subiculum showing radiation of fibers. 



Fig. 5. — Drawing showing diseased mesophyll cells surrounding pycnidium. 



Fig. 6. — Young pycnidium before spores are formed, showing covering 

 layer and conidiophores. 



Fig. 7. — Pycnidia showing shape and relation to host: shading indicates 

 diseased cells. 



Fig. S. — Detail of pycnidium with spores. 



Fig. 9. — Conidia germinating, with appressoria. 



Fig. 10. — Pycnidium and perithecium produced from same mycelium: 

 shading indicates diseased region. 



PLATE XVI 



Figs, ua-iib. — Perithecia showing typical dome shape. 



Fig. 12. — Detail of perithecial wall. 



Fig. 13. — Perithecium in early development with merely a bed of hyaline 

 mycelium below the covering. 



Fig. 14. — Perithecium showing asci and paraphyses ; diagrammatic. 



Fig. 15. — Young perithecium showing progressive thickening of cells and 

 basal structure. 



Fig. 16. — Pycnidium resting on dermal subiculum: second shaded area 

 represents diseased mesophyll cells. 



Fig. 17. — Asci and spores. 



Fig. iS.— Top view of covering wall of pycnidium and of subiculum showing 

 radiate character. 



Fig. 19.— Very young infected area: only mesophyll cells diseased. 



