218 THE NEW AGRICULTURE. 



to carry on warfare with an enemy that you know nothing of, 

 and of whose identity you are uncertain, but once have him cor- 

 nered as we now have the enemy of the pear, we shall no longer 

 fear him. Our space will not permit giving a full description of 

 Professor Arthur's thorough investigation. Suffice it to say that it 

 was thoroughly convincing. He has found that bacteria can be con- 

 veyed to the pear only when the young wood is exceedingly "soft, 

 and never through old wood, or that which has become hardened, 

 except it be through the young and immature twigs. Thus the 

 bacteria may be conveyed to the older wood only through the bac- 

 teria that enters the tender wood. The bacteria enters the trees 

 in July, and hardly ever in August or later. The bark of the 

 branch attacked may be destroyed several weeks before the leaves 

 turn black, as the leaves are sustained by the w r ood of the branch. 

 Usually the leaves turn black suddenly during a hot day. This is 

 the first notice the orchardist has of disease, but really the damage 

 has been done weeks before. Bacteria do not enter the branches 

 by contact of diseased branches with healthy ones, neither are 

 they conveyed by the pruning knife. The bacteria gain entrance 

 to the trees through the young and tender wood, through the blos- 

 soms, or through the fruits in rains, or conveyed by the winds, 

 Also possibly by evaporation of moisture from the soil in which 

 they have been multiplied. Bacteria progress through the limbs 

 more rapidly in the warmest weather. They are not killed 

 by the cold, but are unable to make such fast progress during 

 winter. Those in the' affected branches work slowly all winter, but 

 perish about the time the trees leave out in the spring. Germs for 

 inoculating bacteria were secured by cutting pieces of blighted 

 wood and placing them in water, or fluid produced by boiling corn 

 meal in water, or hay tea. Soon the liquid was filled with the 

 germs. A few of these inserted in the tender wood caused dis- 



