MISCELLANEOUS PAPERS. 423 



be supposed that apple and cedar trees, belonging as they do to totally 

 different families, would be mutually helpful ; but in this case there 

 happen to be other biological reasons why they should not be culti- 

 vated together. Apple and cherry, apple and peach, or apple and 

 pear should not be cultivated close together, as they both belong to 

 the same botanical family, both secrete prussic acid, and both ex- 

 haust the soil of the same chemical ingredients, materials not in the 

 soil in too great abundance, and not at all in some soils. That ex- 

 plains, too, why apple or fruit-trees do not do well in certain soils, 

 and why orchards die out, and why young apple trees will not grow 

 where an old apple tree has died out. Other crops may do well there. 

 It also explains why, in Maryland and eastern Virginia, after the 

 original hardwood forests have been cleared away, or after the land 

 has been cropped to exhaustion, nothing but pines grow ; and why, 

 in Michigan and elsewhere, after the native pine forests are cleared 

 away, the land quickly becomes covered with a luxuriant growth of 

 oaks, maple, beech, and other deciduous trees. 



WATER FOR POTABLE USES. 



Spring- or well-water, containing a small percentage of lime, the 

 smaller the better, so that there is some, seems to be best for potable 

 and culinary uses. Rain-water is not best unless well filtered, for 

 the reason that it contains much that is deleterious, such as decaying 

 insects and their remains ; decaying pollen, spores, and other vege- 

 able particles; sand, chalk, and other earthy substances; ammonia, 

 smoke, carbonic acid, and other noxious gases; bacteria, parasites, 

 and the germs of numerous diseases, besides the unspeakable filth 

 that accumulates on roofs between rains. These are all beneficial to 

 vegetation, but are filtered out of it by the earth largely before it 

 sinks eight inches, and almost wholly before it sinks eighteen feet, 

 into the earth. Water falling at the close of a prolonged rain is 

 purer; but water standing in rain barrels, cisterns, etc., generally 

 teems with microscopic plants and microzoa. 



Water containing much soda, potash, gypsum or salt, is not good; 

 but usually it is not necessary to drink such waters, as there are few 

 places in the Missouri and upper Mississippi valleys where good po- 

 table water may not be obtained. Surface-water that has stood for 

 several days should not be used. Creek or river waters may be used 

 if far enough below any source of pollution for the waters to become 

 thoroughly aerated in transit ; otherwise boiling is beneficial or may 

 even be necessary. Water obtained from shallow wells, or from 

 within three feet of the surface, should not be used unless the source 

 be subterranean, as in a spring. 



If there be any source of contamination in a neighborhood, the 



