INOCULATION" EXPEKIMENTS. 75 



varieties of the same host show great differences in susceptibility to 

 any particular race of the fungus, it is clear that success or failure of 

 inoculation experiments may depend, in many cases, on some of these 

 factors. Further discussion of this subject will be found under the 

 heading "Parasitism of Glomerella." Proper conditions of tempera- 

 ture and moisture are also necessary for successful infection either by 

 surface application or puncture. Negative results from inoculation 

 experiments with spores applied to the uninjured surface of a host 

 can not be regarded in all cases as sufficient evidence that the plant is 

 not susceptible to the disease, as the infection may really occur but 

 not develop further at the time for lack of proper temperature, 

 moisture, or host conditions. 



In the inoculation experiments in which fruit was used, it was, in 

 most cases, nearly or quite mature. The specimens were always 

 thoroughly washed with corrosive sublimate, 1 to 500, to destroy any 

 spores which might be present on the surface. They were then rinsed 

 with distilled, or sterile, water, and placed in a sterile chamber. A 

 small beaker of water was also placed in the chamber to afford a slight 

 amount of moisture. Unless otherwise stated, the fruit inoculations 

 were always made on picked fruit with a sterilized needle, conidia or 

 ascospores being inserted in a small puncture through the skin. 

 Checks were used which remained free from rot in all cases except 

 where some special statement is made to the contrary. 



APPLE TO APPLE. 



Various inoculations of apples were made at different times by the 

 writers, conidia of Glomerella from different races or strains being 

 used, in order to compare the rapidity of their development and the 

 effect upon the host. In all the cases in which the inoculations were 

 made by punctures, infection occurred and decay followed. The 

 fruit had the usual appearance of bitter-rot, and acervuli were usually 

 produced. The spots developed to about 1 centimeter in diameter in 

 a week. In some cases development was slower than when inocula- 

 tions were made with conidia from other host plants. 



In three series of experiments conidia were applied to the unbroken 

 skin of nearly mature apples. In none of these cases did any rot fol- 

 low, although the fruit was kept in a moist chamber for a long period. 



Sound apples were inoculated by puncture, using conidia from a 

 single spore culture of the chromogenic form of the apple Glomerella, 

 which has already been described on page 39. Rot developed about 

 each puncture with about the same rapidity as in other cases and 

 acervuli were produced in about three weeks. 



Clinton (19) reports successful inoculations of green fruit on trees 

 by inserting conidia in punctures, as indicated in Table IV. He also 



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