Feb. i, 1921 



Onion Smudge 



697 



A similar study of growth in tubes of onion decoction was made, with 

 essentially parallel results. The optimum on this medium appeared to 

 be slightly higher (27 to 29 C.) and slight growth occurred at 31 . 



SPORE GERMINATION 



Relation OF medium. — For the studies upon spore germination a 

 few drops of the liquid medium to be used were placed in Van Tieghem 

 cells. A suspension of conidia in the same liquid was made, and a drop 

 of this was transferred to cover glasses, which were then inverted over 

 the cells and partially sealed with 



S» 



si 



Vivo 



s 





Fig. 



vaseline. The preparations were 

 placed in Petri dishes and exposed 

 to the desired conditions. For 

 some purposes open drops on glass 

 slides placed in Petri dishes lined 

 with moistened filter paper were 

 more suitable. 



A comparative study of spore 

 germination in distilled water, 

 onion decoction, 1 onion leaf ex- 

 tract, 2 onion scale extract, 3 soil extract (sterilized and unsterilized) , 4 

 and soil decoction 5 was made. 



At room temperature germination in favorable liquid medium began 

 within 5 to 6 hours. At 24 hours practically all viable spores had germi- 

 nated. The percentage of germination in the drops was determined by 

 averaging the counts of several microscopic fields. The results of these 

 tests are summarized in Table I. 



Table I. — Effect oj various media upon spore germination of Colletotrickum circinans 



£ /O /S SO 3S OO 



4. — Relation of temperature to growth of 

 Colletotrickum circinans on agar plates. 



Medium. 



Distilled water 



Soil decoction 



Soil extract, sterilized 



Soil extract, unsterilized 



Onion decoction 



Onion leaf extract 



Onion leaf extract, diluted with distilled water 1 to 10. 



Onion scale extract 



Onion scale extract, diluted with distilled water 1 to 10 



Percent- 

 age of ger- 

 mination. 



60 



95 

 95 

 10 



99 



1 Onion decoction: ioo gm. onion scale in 500 cc. distilled water steamed one hour, filtered, and sterilized. 



2 Onion leaf extract: Fresh onion leaves (green) crushed and the sap extracted by squeezing through 

 cheesecloth. 



1 Onion scale extract: Fresh onion scale crushed and the sap extracted as in onion leaf extract. 



4 Soil extract: 500 gm. black loam soil was supported in a glass funnel by excelsior and absorbent cotton: 

 500 cc. of tap water were poured over the soil; the filtrate was collected twice, and each time it was poured 

 over the soil. The third filtrate was divided into two parts; one part was left unsterilized and the other 

 part was sterilized in tubes at 15 pounds pressure for ]4 hour. 



5 Soil decoction: soo gm. of black loam soil, to which had been added 500 cc. of distilled water, was steamed 

 at is pounds pressure for 14 hour. The liquid was filtered through filter paper and sterilized in tubes at 

 i; pounds pressure for yi hour. 



