The Reason for Rotation in Crops 23 



until fields of their favorite food plant increased their 

 broods. 



Some crops supply humus either through the parts 

 left on or in the soil, or through the mulch used to retain 

 moisture, as in the case of potatoes. 



Some plants feed through fibrous roots which ramifj^ 

 near the surface, while others extend their roots more 

 deeply, draw their food supply from lower strata and 

 even from the subsoil. 



Legumes, such as beans, peas, etc., collect nitrogen 

 from the air, not only thus contributing to their own 

 growth, but leaving the soil supplied with this element 

 for the use of future crops — they are nitrogen-collectors. 

 The majority of our garden vegetables are nitrogen-con- 

 sumers, and derive this element of their food from the_ 

 soil. As far as practicable, therefore, nitrogen-collectors 

 should follow nitrogen-consumers, and vice versa. Some 

 garden crops are more favorable to the growth of weeds 

 than others. These should not succeed each other, but 

 should rather be alternated with clean culture crops. 



Neither grass nor weeds should ripen seed in a gar- 

 den if possible to prevent it. Large quantities of grass 

 and weed seeds are introduced into the garden in home 

 manures not properly fermented. 



All of these manures should be composted with acid 

 phosphate and allowed to ferment in heap until the 

 germs of all seed which they contain are destroyed. 



Plants of the same species should not succeed each 

 other. Plants grown for their seed, or for fruit in which 

 the seed are developed, should follow and be followed by 

 those grown for their leaves. 



