22 The Principles of Fruit-growing. 



plant or the part affected. Such troubles are peach 

 yellows, and black -knot of the plum and cherry. A 

 law cannot be enforced unless public sentiment is 

 behind it, and when public sentiment is aroused the 

 law is not needed. Yet a law is often useful for a 

 time to awaken public sentiment and to call attention 

 to the evil. The final recourse is always greater 

 knowledge and enlightenment. 



There are also insurmountable difficulties in the 

 enforcement of laws designed to control the spread 

 of noxious insects and fungi, because it is practically 

 impossible to detect the eggs of insects or spores 

 of fungi upon a large number of plants, and because 

 there are" so many natural and uncontrollable ways 

 in which the parasites may spread. The original 

 Maryland law, designed to prevent the introduction of 

 fruit-tree diseases and pests, was a case in point. 

 It required that "whenever any trees, plants or vines 

 are shipped into this state from another state, every 

 package thereof shall be plainly labeled on the out- 

 side with the name of the consignor, and a certifi- 

 cate showing that the contents had been inspected 

 by a State or Government officer, and that the trees, 

 plants or vines therein contained are free from all 

 San Jose scale, yellows, rosette and other injurious 

 insect or disease." It would be impossible for any 

 botanist to certify that a dormant tree were free of 

 all disease ; and even in the matter of San Jose 

 scale, an entomologist could not give a clean bill 

 of health without giving more time to the examina- 

 tion of a tree than it is worth, In the operating of 



