xvi Journal of Agricultural Research voi.xx 



79. A. — Typical conidiophore, showing characteristically long, slender, un- 

 knobbed basal cell, relatively short main axis with its greatest diameter 

 about midway to the primary branches, and fairly well-developed branch 

 system bearing long, slender conidia. B. — Upper portion of a conidio- 

 phore which has a poorly developed branch system and hence bears 

 few conidia on sterigmata which are relatively large. C. — Portion of the 

 branch system of a conidiophore, showing the conidia germinating while 

 still attached to their sterigmata. D. — Stalk portion of a typical conidio- 

 phore, showing long, slender, unknobbed basal cell, and main axis which 

 is slender above the septum, expands rapidly to its greatest diameter 

 about midway, and contracts again below the branches. E, F. — Typical 

 basal cells of conidiophores. G. — Stalk portion of a conidiophore with 

 basal cell which, though unusually short, nevertheless is longer than the 

 extent of the main axis from septum to primary branches. H. — Typical 

 stalk portion of a conidiophore from sugar cane. I, J, K. — Typical 

 conidia showing variations in size and shape and method of germination Page 

 by hyphae 684 



Onion Smudge 

 Text Figures 



1. Conidia and appressoria of Colletotrichum circinans 689 



2. Acervulus of Colletotrichum circinans on artificially inoculated onion scale . 690 



3. Spores of Colletotrichum fructus (A) and C. circinans (B) 694 



4. Relation of temperature to growth of Colletotrichum circinans on agar plates. 697 



5. Relation of temperature to spore germination of Colletotrichum circinans. . . 698 



6. Colletotrichum circinans: Stage of penetration of epidermal cell of onion 



scale at 66 hours after inoculation 702 



7. Cross section of epidermis, showing early stage of penetration by Colletotri- 



chum circinans 7°3 



8. Cross section of epidermis (A ) and underlying parenchyma cells (B) of onion 



scale inoculated with a suspension of Colletotrichum circinans spores and 



kept in a moist chamber at room temperature 704 



9. Cross section of onion scale naturally infected with Colletotrichum circinans, 



showing the mycelium developing first just beneath the cuticle and later 



penetrating the subcuticular wall 7°5 



10. Chart from data collected at Racine, Wis., during 1915 and 1916, showing 



the daily mean soil temperature at a depth of 1 to 2 inches, and the rainfall . 708 



Plates 



80. Onion smudge: Onion sets (White Portugal variety) naturally infected with 



Colletotrichum circinans 7 22 



81. Onion smudge: A, B, E, D. — Advanced stages of smudge after several 



months in storage. C. — Bulb inoculated in a moist chamber with a sus- 

 pension of Colletotrichum circinans conidia. F, G. — Macros porium sp. on 

 outer scale of white onion sets. H. — M. porrum and Phoma alliicola on 

 outer scale of white onion set 7 22 



82. Relation of soil temperature to the development of smudge 722 



83. Colletotrichum circinans and C. fructus: A. — Photomicrograph of cross section 



of naturally infected onion scale. B. — Photomicrograph of cross section 

 of an infected onion scale held for several months in poorly ventilated 

 storage. C, D. — Photomicrographs of cross sections of C. circinans (C) 

 and C. frutus (D) on apple fruit 7 2 » 



