224 



SCIENCE 



N. S. Vol. XXX. No. 763 



trace of the yellow slime in the bundles of the 

 stem, although most of the plants so included 

 contained very few affected bundles and did not 

 yet show distinct secondary signs. In the plants 

 grown from untreated seed there were many severe 

 cases of the disease, the entire foliage being dried 

 out and the bacterial multiplication in the vessels 

 of the stem being several thousand times as much 

 as in the cases which appeared in the treated 

 plants. The seed corn was considered as sus- 

 picious for two reasons : ( 1 ) earlier in the season 

 some plantings in Virginia made from this par- 

 ticular sample yielded many diseased plants, and 

 (2) the corn was grown by a man to whose farm 

 the writer traced a similar outbreak of this dis- 

 ease some years ago. 



Various yellow bacteria were obtained from the 

 surface of this corn by means of agar poured- 

 plates, but not Bacterium Stewarti, although 

 many attempts were made to isolate it. The 

 latter consequently could not have been very 

 abundant, at least in a living condition, and this 

 may in part account for the small number of cases 

 obtained (10 per cent.). The total cases on the 

 untreated plots were 185 out of 2,017 plants; on 

 the treated there were 36 cases out of 2,370 plants, 

 32 of these cases being only slightly diseased. 



The Occurrence of Bacterium pruni in Peaoh 



Foliage: Ebwin F. Smith. 



Some years ago the speaker made inoculations 

 (by spraying) on the foliage of some peach trees 

 standing in his back yard. The schizomycete used 

 was derived from the black spot of the plum. 

 The sprayings were made late in July, at sunset 

 in rather dry weather. The trees were not cov- 

 ered by tents and the spraying was not continued 

 through the night, as it should have been. The 

 next morning the foliage was dry. After some 

 days, a few bacterial leaf spots developed on one 

 of these trees — perhaps fifty altogether, and a 

 microscopic examination demonstrated the pres- 

 ence of pockets of bacteria in some of these spots, 

 but the experiment was considered in the light of 

 a failure because very few spots appeared in pro- 

 portion to the amount of culture fluid used, and 

 none at all on one of the trees. Subsequent 

 studies on plums led to the belief that the rea- 

 son for this failure was due to the age of the 

 foliage and to the fact that the moisture did not 

 remain sufficiently long to secure many infections. 

 In the summer of 1907 these experiments were 

 repeated in one of the hothouses of the Depart- 

 ment of Agriculture under conditions which could 



be more readily controlled. Healthy seedlings and 

 grafted plants of two ages were placed close to- 

 gether on a bench in one corner of one of the 

 hothouses, and heavy canvas was hung in front 

 of the two exposed sides of the bench, so as to 

 make an enclosed area which could be kept moist. 

 River water was then syringed upon the plants 

 (the same that the plants had been in the habit 

 of receiving) and afterwards water dilutions of 

 pure cultures of Bacterium pruni, obtained from 

 Arkansas plums. The tent cloth was kept on for 

 two days and the sprayings were repeated at 

 intervals, so that with the exception of two short 

 periods during which the foliage became dry by 

 accident, the moisture was retained upon the 

 leaves throughout the time that the tent cloth was 

 employed. The result of this experiment was the 

 appearance, after a number of days, of several 

 thousands of typical leaf spots. A microscopic 

 examination of many of these spots demonstrated 

 a great number of bacteria in the center of the 

 same, and poured-plate cultures were made there- 

 from. To obtain numerous spots it is necessary 

 to make inoculations early in the growing season, 

 that is, in May, and to keep the foliage moist from 

 twenty-four to forty-eight hours. The spots ob- 

 tained on the peach leaves differed in no way 

 from those occurring naturally on peach, and 

 there can be no doubt that the leaf spot of peach 

 is identical with that of the black spot of the 

 plum, both being due to Bacterium pruni. All of 

 my experiments, however, have been made with the 

 organism taken from the plum. 

 Two Sources of Error in the Determination of 



Gas-production hy Microorganisms: Ebwin F. 



Smith. 



1. Some microorganisms produce gas from in- 

 osit (muscle sugar), consequently in bouillon 

 agar shake-cultures, to which various sugars have 

 been added, the resulting gas bubbles can not be 

 attributed to the sugar added until it is known 

 (a) that inosit does not occur or (6) that the 

 organism is incapable of fermenting inosit. 



2. Some gas-forming microorganisms, e. g., a 

 yeast recently isolated by the writer, do not lib- 

 erate gas unless the cultures are shaken or stirred, 

 e. g., with a platinum needle. Then gas is evolved 

 abundantly. Ignorance of this fact might some- 

 times lead to error. It is a fact well known in the 

 Caucasus that the kefir ferment takes place most 

 satisfactorily "if the leathern sacks are frequently 

 shaken, and it is said to be the habit for each 

 member of the family to give the sack a kick in 

 passing by it. 



