110 BACTERIAL DISEASES OF PLANTS 



Ice Boxes. — Stock cultures must be kept at low tempera- 

 tures. They live much longer when cool and thus the labor of 

 transfer, which is always considerable in any laboratory dealing 

 with many organisms, is minimized. 



Our stock cultures are kept in ordinary refrigerators such 

 as housewives use. This corresponds probably to the practice 

 of many other laboratories but it is not the best way, since 

 occasionally through carelessness on the part of the ice man or 

 of servants the outlet becomes stopped up or the floor support- 

 ing the ice becomes cracked and water drips down on some of 

 the cultures, destroying them or at least contaminating them 

 so that they must be plated out. A better way would be to 

 keep stock cultures in a thick-walled roomy vault constantly 

 supplied with cooled air. 



Ice Thermostats. — We make frequent use of the Paul Alt- 

 man device containing ten small compartments. This, when 

 the upper large chamber is filled morning and night with cracked 

 ice, gives temperatures ranging, except during about four months 

 of our year (June to September), from 0.5°C. to 20°C. These 

 temperatures are not absolutely constant under our room con- 

 ditions, but would be nearly so in a room having itself a fairly 

 constant air temperature. By looking frequently and adding 

 more ice if the temperature is observed to be rising, we are en- 

 abled to make much use of it in determining lowest temperature 

 at which seeds will germinate, microorganisms grow, etc. It is 

 not, however, a perfect instrument. 



STUDY OF CULTURES 



All the various plant pathogenic bacteria should be grown 

 on a great variety of media for discovering special characteristics, 

 useful in identification, and also to determine the media best 

 suited to their growth and longevity. These cultures should be 

 examined frequently with the hand lens in a variety of lights, and 

 often under the compound microscope, and should not be dis- 

 carded for several weeks. Of course, checks should be held. 

 To what I have said in other places, I would add here that 

 colonies on agar and gelatin plates should be photographed in 



