124 



BACTERIA IN RELATION TO PLANT DISEASES. 



least inconvenience is by storage in cool boxes (refrigerators) at temperatures of 10 

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

 transfer, and even sensitive organisms will generally live for some months, especially 



B 



Fig. 115* 



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

 collection of dead bacteria on culture media to serve as museum specimens, but it 

 is possible to do so, it is said, with 

 considerable success by following the 

 methods described by Hauser and 

 others (Bibliog., L,II). 



DISTILLED WATER. 



All laboratories doing much work 

 should have an abundance of distilled 

 water, and where this is not readily 

 obtainable in sufficient quantity and 

 of good quality, provision should be 

 made for it when the laboratory is 

 constructed or when the necessity 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. 116.t 



*Fic. 115. Cross-section of tooth of cabbage-leaf infected by Bacterium campestre. Plant No. 

 401 sprayed with water containing an agar-culture. Bacterial occupation 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 ft below the apex of the leaf-tooth. A few micromillimeters further 

 down (370 >u) all trace of the bacteria disappears. 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- 

 ing fluid from the water-pores. Actual length of section, slightly under I millimeter. Slide 331 3 

 Plant sprayed December 9, 1904; slightly blackened leaf-tooth fixed 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 catnpestre. 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 it tight, and, of course, spoiled the water for all delicate work. 



