86 



BACTERIA IN RELATION TO PLANT DISEASES. 



i. I?., commonest in southern Italy, Sicil}', and i\lgeria, lies between 32° and 38° C. 

 In m}' own experiments with this organism, obtained from olive trees in California, 

 I have found its maximum temperature to be above 35° and below 37-5° C. The 

 optimum temperature of Bacterium solanacearum, which is very destructive to 

 potatoes and tomatoes in the southern United States, is probably about 35° C. — at 

 least it grew readily and remained alive for a long time in bouillon kept at 37° C. 

 Its maximum temperature is 39 +° C. Bacillus carotcmorus, one of the best known 

 of the soft-rot organisms, grows well in the thermostat at 33° to 34" C. Its maxi- 

 mum teinperature is at 39° C. or slightly below (Jones). Bacillus aroidecz, whose 

 temperature relations were recently studied carefully by Townsend, has a maximum 



Fig. 71.* 



temperature of 41° C. A temperature of 40° C. retards growth, but does not prevent 

 it. This organism was isolated from calla-lily conns, but is capable of causing a 

 soft rot in potatoes, carrots, turnips, and many other plants (fig. 102). The maxi- 

 mum temperature of Bacillus oleraceae, recently described by Harrison, is said to 

 be about 42° C. This causes a soft rot of cauliflower. 



The range of temperature suited for the growth of particular bacteria varies 

 greatly. Some species are able to grow through a range of 50° C. Many tolerate 

 a range of only about 30° C. Certain animal-pathogenic forms have through long 

 subjection to a peculiar environment become restricted to a still narrower range. 



*FiG. 71.— Bacterium pruni. Early stage of a leaf-spot in the plum. The small spot was water- 

 soaked in appearance, but it had nut yet collapsed. The bacteria, which are most abundant in the 

 mesophyll, undoubtedly entered the leaf llirough the stomata, three of which are shown in the section. 

 Material treated as in fig. 70. Section drawn with the aid of an Abbe camera. It represents as 

 nearly as possible one plane. 



