94 



BACTERIA IN RELATION TO PLANT DISEASES. 



GENERAL CONSIDERATIONS. 



Location of the Laboratory. 



If possible, the laboratory should be in a clean building in the middle of a green 

 lawn. If it must be in a crowded and dirty cit}' it should be on an upper floor, as 

 far removed as possible from the dust of the street and from the tramp of feet. It 

 ought not to be located on streets filled with the dust of heavy traffic. If a ground- 

 floor or basement room in a dirt}' localit}^ is the only available place, then the air 

 which enters the room should be filtered through absorbent cotton. A south front 

 is desirable for the mounting of a heliostat and for other photographic purposes ; 

 a north light is desirable for microscopic use, if one is to work at the instrument 

 continuously. By arranging one's time according to the position of the sun, the 

 light from east or west windows may be used to advantage five or six hours a day, 

 which is quite long enough to fatigue ordinary eyes. The writer has managed to 



get along very well without 

 north light for the last ten 

 years. If one decides to use 

 with the microscope only ar- 

 tificial light, such as that of 

 the Welsbach burner, work- 

 rooms for this purpose may 

 be located anywhere. If pos- 

 sible, several rooms should 

 be secured and apportioned 

 to the various kinds of work, 

 ^.^., general laboratory rooms, 

 chambers for special workers, 

 sterilization-room, thermo- 

 stat-room, cold-storage and 

 stock-culture rooms, storage 

 rooms for chemicals, small 

 glass-inclosed rooms for transfer of culttires, photographic rooms, dark rooms for 

 developing, etc. The general photographic rooms should have overhead light as 

 well as side light. 



Equipment oe the Laboratory. 



Many pieces of apparatus may be procured from time to time, as the exigencies 

 of the work demand or as the funds will pennit. Other apparatus must be provided 

 on the start, and some of it when the building is constructed or reconstructed. 



Fig. 79.^ 



*Fic. 79. — Small portion of a cabbage leaf from Long Island, New York, showing characteristic 

 water-pore infections due to Bacterium campeslre. The blackened veins correspond to the location 

 of the bulk of the bacteria which have gained entrance to the vascular system of the leaf by way of 

 the groups of water-pores situated on the serratures of the leaf, particularly those which are conspic- 

 uously blackened. Those parts of the leaf where only the larger veins are shown were green and 

 normal in appearance. Coll. July i6, 1902. Drawn from a photograph. 



