10 The Coeorado Experiment Station. 
not carried on the wind, neither is it traceable to the soil. Ants, 
flies, and possibly bees may feed on the gummy material which runs 
out from the cracks in the diseased wood, and knowing that this 
exudate contains millions of germs, it is only reasonable to believe 
that these insects carry the disease on their feet and bodies to the 
healthy trees. Alighting on a delicate flower cluster, they crawl 
deep down after the so-called honey or nectar in the blossom and 
here many of the blight germs are brushed off and left in contact 
v/ith the tender blossom. Through these honey ducts or nectaries 
the bacteria gain entrance to the plant. Once favorably situated, 
they multiply and move down the twig between the bark and 
woody cylinder through the growing layer. It is in this 
way that a large percentage of the cases originate. As 
further evidence of this method of infection, we may 
cite the investigations of Mr. M. B. Waite, of the U. S. Department 
of Agriculture, who found the germs developing in the nectar of 
the blossoms and also discovered them adhering to the mouth parts 
of honey bees after they had visited infected flowers. He further 
observed that, in many cases, trees which did not blossom were free 
from blight. 
Again, the germs may gain entrance into the tender shoots 
through insect bites in the bark, for, although the opening may be 
no larger than a pin prick, myraids of bacteria can find a temporary 
dwelling place in this wound and may soon spread through the 
whole member. Lastly, the infection may enter the large limbs and 
trunk of the tree by some scratch or bruise in the protecting bark 
which has exposed the susceptible growing layer beneath to the 
visits of germ-laden insects. 
Thus we see that pear blight is caused by a germ to which the 
name Bacillus amylovorus (Burrill) has been given, the meaning of 
which is starch destroying. We see that it is spread from one tree 
to another by different insects, and that the germs may gain en¬ 
trance into the plant in any of three ways: First, and most impor¬ 
tant, through the blossom; second, through insect bites in the tender 
shoots; third, through mechanical injuries to the bark of the limbs 
and trunks of the trees. 
Conditions Favoring the Disease. —Although the knife is 
oui only hope of exterminating the blight, there are undoubtedly 
conditions which favor the disease. 
It is a matter of common observation that climatic conditions 
have a marked influence; warm, moist weather with a large amount 
of rainfall favors it, while bright, dry, cool weather tends to check 
it. That is, the former conditions are advantageous to the growth 
of the germs, while the latter are unfavorable. 
High cultivation, rich soil, heavy manuring, the use of large 
