March, 1936] Agricultural Research in N. H. 15 



Hemolytic Streptococci in Pasteurized Milk 



It has been found that hemolytic streptococci are much more prevalent 

 in pasteurized milk than is commonly supposed. Samples of such milk with 

 standard plate counts of only 5000 bacteria per millilitre have been found 

 to contain in addition, when an appropriate culture medium was used, from 

 1,000 to 50,000 hemolytic streptococci per millimetre. Morphological and 

 cultural studies of the organisms isolated have been made. (L. IV. Slanetz- —  

 Hatch Fund.) 



Effect of Place on Mosaic and Leaf-Roll 



Due to toxic soil used in 1933 the series of experiments on mosaic and 

 leaf -roll plants grown at a mean temperature of 20° C. and 15°C. was broken 

 due to the loss of cultures grown at 15°C. 



Most of the plants grown at 20° C. were, however, saved and in 1934 

 work with complete sets was resumed. At the same time a new series com- 

 prising healthy and mosaic plants was started to verify the results obtained 

 with the first series. 



During the period covered by this report the 6th generation of cultures 

 of the original series was grown, and the second generation of the second 

 series. 



One of the main features of the work has been the study of the effect of 

 growing cultures continually at 20° C. and 15°C. and the effect of moving 

 the cultures from one year at one of these temperatures to the other tem- 

 perature the following year. 



So far the healthy or mosaic plants have shown no tendency to run out, 

 though a change in temperature from one year to the next does affect the 

 yield. In the case of leaf roll there is very definite deterioration and at pres- 

 ent after six generations there is hardly a plant left. It made no particular 

 difference whether the cultures were moved from year to year or kept at the 

 same temperature. During the year there were only 17 leaf -roll plants grow- 

 ing at 20° C. and 17 growing at 15 °C. Had there been no deterioration there 

 would have been a total of 234 plants instead of 34. At the end of the grow- 

 ing season only four plants in the series grown at 20° C. and four plants in 

 the series grown at 15°C. produced tubers of a maximum weight of not less 

 than 40 grams. 



The seed pieces or leaf roll plants grown at 20° C. were hard when the 

 cultures were harvested in 23 per cent of the plants, but in the cultures 

 grown at 15°C. 70 per cent of the seed pieces were hard. 



Moving leaf -roll plants from 20° C. to 15°C. caused an increase in yield 

 in the majority of cases. 



In the case of the cultures of mosaic plants there has been no tendency 

 to run out and yield at 20° C. was in general higher than at 15°C. 



In the case of the healthy plants we found in the first series that growing 

 cultures one year at 20° C. and removing them the next to 15°C. the yield 

 obtained was not so high as in the cultures that had remained continuously 

 at 15°C. and that two years were required to bring the yield up. In the case 

 of the second series of healthy plants we secured during the year partial 

 confirmation of the results secured with the first series. (0. Butler — Purnell 

 Fund.) 



