STATE POMOL'^GICAL SOCIETY. 49 



These germs are so very minute as to require the highest powers 

 of the microscope to detect them. So small are some forms that it 

 is claimed a globular mass that would pass through the eye of a 

 cambric ueedle might contain 20,000,000 of these living, growing 

 organism. 



The lightest breath of air may disturb them and carry them long 

 distances. They may be sa'd to be ever3'where. As man}' as 11,000 

 have been found floating in a cubic metre of air, and 80,000,000 

 have been found in a quart of ordinary water. 



The blight of the pear and the twig blight of the apple and quince, 

 are caused or accompanied by a very rapid development of very 

 minute germs, (microccccees amylovoms) which are oval in form > 

 about 55J50 of an inch long by 55*55 in diameter, and closely related, 

 in form and method of development, to those producing contagious 

 diseases in animal tissues, as the small-pox, diphtheria, hog cholera, 

 glanders, etc. 



PEAR BLIGHT. 



In some sections and some seasons it is more prevalent than in 

 others. The first appearance of it may be seen b}' black spots on 

 the bark of the shoots or by the leaves turning almost black, and 

 so rapid is its work, that it requires but a short time to destroy large 

 branches and often the whole tree. 



It very seldom attacks all the trees in an orchard or all the varieties 

 alike at one time, but we see a branch here or a tree there affected 

 and perhaps one only of a large number of the same kind in a row, 

 showing that it cannot be classed as a very contagious disease as is 

 claimed by some 



I shall take the ground that it is not contagious to healthy trees, 

 but like so many of similar organisms which attack animal tissues, 

 it only develops when the cells of the plant are in a proper stage 

 or condition to furnish the necessary food. It is stated by Prof. 

 W. S. Farlow, the noted mycologist, that the germs have been found 

 in healthy tissues and did not cause the disease or blight, just as 

 the germs of diphtheria and hydrophobia have been found in the 

 throats of persons who were not attacked by either disease. 



The germs may enter through crevices of the bark, through the 

 delicate tissues of the blossoms or through the stoma of the leaves, 

 but if the tissue is in a vigorous, healthy condition, it will resist 



