HOW PLANTS ARE INFLUENCED 351 



Some plants are found only in sour humus (either 

 in wet humus, as Peat Mosses, Sundew, etc., or in dry 

 humus, as Heath plants) , while others are found only in 

 "mild" humus (Dog's Mercury, Cow Wheat, etc.): 

 some, indeed, are found only in a particular kind of 

 humus, e. g., that of Conifers (Rattlesnake Plantain). 

 Observe all you can in regard to the occurrence of 

 plants in different kinds of soils. To a certain extent 

 each kind of soil is characterized by certain plants. 

 This has been noticed by prospectors, who have found 

 that certain plants are found only where certain metals 

 (e. g., zinc) abound. 



A fuller understanding of the kind of soil preferred 

 by different plants 1 will not only enable us to better 

 suit our crops to our land, but be of great assistance in 

 determining the availability of hitherto uncultivated 

 land for various crops. 



Not only the chemical, but more especially the 

 physical character of the soil and of the subsoil 

 (whether hard-pan or porous), is of importance in this 

 connection. Find out what kind of land is considered 

 most suitable for the various crops with which you are 

 familiar. Try also to cultivate the ability to judge of 

 the character of the land by the wild plants which grow 

 on it. Such plants are indicators not only of the 

 chemical and physical character of the soil, but also of 

 the temperature and other important factors of climate. 



1 The United States Department of Agriculture is now making soil surveys 

 in various states, to determine what crops are best adapted to various soils. 



