124 



BACTERIA IN RELATION TO PLANT DISEASES. 



least inconveuience is by storage in cool boxes (refrigerators) at temperatures of io° 

 to 15° C. By tliis method some organisms can be kept alive on agar a year without 

 transfer, and even sensiti^'e organisms will generally live for some months, especially 



Fig. 115. 



if planted in proper media. The writer has never made any attempt to prepare a 

 collection of dead bacteria on cidture media to seiv-e as museirm specimens, but it 

 is possible to do so, it is said, with 

 considerable success by following the 

 methods described by Hauser and 

 others (Bibliog., LII). 



DISTILLED WATER. 



All laboratories doing mucli work 

 .should have an abundance of distilled 

 water, and where this is not readily 

 obtainable in sirfficient quantit)' and 

 of good quality, provision should be 

 made for it when the laborator}' is 

 constructed or when the necessit}- for 

 it arises. In the construction of such 

 a still many things must be kept in 

 mind, if it is to work satisfactorily 

 and yield water of the desired purity. J 



*FiG. 115.— Cross-section of tooth of cabbage-kaf infected by Bacterium camfcslrc. Plant No. 

 401 sprayed with water containing an agar-cnltnre. Bacterial occnpation limited to points between 

 A and B. At X vessels are occupied. At A and B the bacteria lie in the intercellular spaces and 

 have not yet entered the vessels. For details of A and B, see figs. 116 and 117. This section, which 

 IS one of a series, was cut 270 /< below the ape.x of the leaf-tooth. A few micromillimeters further 

 down (370/O all trace of the bacteria di,sappears. In other words, the bacteria are still confined to 

 the leaf-tooth, and there is no cavity like that shown in fig. 76. When sprayed this leaf was extrud- 

 mg fluid from the water-pores. Actual length of section, slightly under i millimeter Slide 331c 3 

 Plant sprayed December 9, 1904; slightly blackened leaf-tooth fi.xed in 95 per cent alcohol on 

 December 17, 1904. Inked from a photomicrograph. 



fFic. 116.— Cross-section of leaf-tooth of cabbage infected by Bacterium eampestre. A detail 

 from fig. 115 at A. The bacteria have not yet entered the vessels. 



tThat thing which has given the writer most trouble was an entirely unexpected difficulty viz, 

 a plague of tiny red house ants. These got into the reservoir in spite of all that could be done to 

 render jt tight, and, of course, spoiled the water for all delicate work 



