SCHIZOMYCETES. BACTERIA 127 



Single cells of the organism direct from the tree are oval, 1.5 

 to 2/j long, and somewhat more than half as broad (Fig. 34). 

 They occur single or attached, several end to end. Upon various 

 culture media they are more commonly single or in pairs, al- 

 though sometimes in short threads, and in 

 all cases motile in fresh cultures. 



On gelatin growth is slow, requiring three 

 to five days for the appearance of colonies, 

 the latter being globose to lenticular, yellow- 

 ish, liquefying the medium very slowly. 



On agar the surface colonies appear more 

 rapidly, being evident the second day, and FlG . 34 . ~~^[ LVS AMY _ 

 attaining a diameter of from 2 to 3 mm. by lovorus from Apple 

 the fourth or fifth day. They are white and Fruit ; Simple Stain 

 granular, or cloudy, with a sharply defined white center ; the mar- 

 gins are entire or slightly wavy, with a dense white center. Immersed 

 colonies are globose or lens-shaped, and opaque-yellowish. 



In bouillon a cloudiness is produced after twenty-four hours, 

 and this is accompanied by slight acidity ; after forty-eight hours 

 there is greater cloudiness, with more or less persistent flocci, 

 the medium becoming alkaline, and in time showing a tendency 

 to clear. In sugar-free bouillon the liquid remains clear for 

 twenty-four hours, except for slight sediment. It is neutral at 

 first, becoming cloudy and alkaline after some days. In milk 

 no change is evident until the third or fourth day, when thick- 

 ening begins, which increases to fifth or sixth day. The product 

 finally becomes subgelatinous, and in ten days there is a clear 

 liquid above. This is at first acid, becoming slightly alkaline. 

 Litmus milk is unchanged. 



On slanting agar tubes growth in twenty-four hours is moderate, 

 opalescent, spreading slowly, producing turpidity in the water of 

 condensation ; growth not viscid. 



On gelatin stab cultures growth is similarly slow, and beaded 

 or granular along the needle path ; surface growth with irregular 

 or erose margin, center thin and granulose ; liquefaction slow, 

 crateriform and stratiform. 



Control. The control of pear blight was for a long time con- 

 sidered impossible, but careful study under various conditions 



