130 OUTLINES OF BACTEEIOLOGY 



A disease affecting olive trees and called Olive tuberculosis is charac- 

 terised by the appearance of irregular nodulose tubercles on the 

 branches, each about J-l inch in diameter. The tubercles superficially 

 resemble the galls of insect origin, but when microscopically examined, 

 they are found to be full of bacteria. The latter belong to Bacillus oleae. 



A somewhat common disease is the black rot of cabbage, caused by 

 Pseudomonas campestris. The infliction of this disease results in a 

 dwarfing or in a one-sided growth of the heads. Not infrequently 

 it may be characterised by the absence of heads altogether. The stem 

 shows brown or black in the woody portion, whilst the other parts 

 become yellow in colour, and the leaves appear as if their edges had 

 been burnt. The germ enters the margin of the leaves through the 

 water pores. These are small openings found at the ultimate termina- 

 tions of the veins of the leaves. The plants are weakened by slugs and 

 caterpillars which feed on the leaves, and as they also bear the bacteria 

 in their bodies, they facilitate the dissemination of the disease. The 

 remedy for this disease is to be found in the institution of a rotation 

 of crops, and by checking the multiplication of slugs and caterpillars. 



The Pink Bacteriosis of wheat is caused by Micrococcus tritici. This 

 germ causes the grains to assume a rose or purple colour. The starch 

 is first removed by this microbe with the result that the grain 

 becomes more or less hollow. Next the gluten and finally the cell- 

 walls are attacked. The bacteria are found in an opaque, colourless, 

 thin, and nodulose layer, lining the cavity of the diseased grain. 



In the northern and southern parts of France, and also in some parts 

 of England, tomatoes are attacked by a microbe which forms black 

 rings in the fruit. These rings extend in widening circles until the 

 whole fruit is destroyed. The investigation of this disease has not yet 

 been satisfactorily accomplished. 



Finally, a disease affecting hyacinths and very prevalent in Holland 

 is caused by a microbe which first attacks the bulbs of these plants 

 when in the resting condition. Later, yellow spots appear on the 

 bulbs and leaves, and a yellow slimy liquid, which teems with bacteria, 

 can be obtained from the inner parts of the plant. 



The scientific investigation of plant diseases is still far from com- 

 plete. The researches that are published on the matter all show that 

 the general conditions affecting the diseases of plants are identical with 

 those that hold in the case of animal diseases. These researches also show 

 that the problem of prevention of plant disease is largely a problem 

 concerning the best means of destroying the creatures that inflict 

 wounds on plants, thus rendering them susceptible to various diseases. 



