ECONOMIC PLANTS 



2OI 



Silo Structures. - - The silo must be air-tight. Bac- 

 teria enter the silo with the fodder and grow and mul- 

 tiply rapidly, as shown by the heating of the mass and 

 the formation of acid in it ; in other words, fermenta- 

 tion begins. If the silage is well packed so as to leave 

 no unfilled spaces and the silo walls are air-tight, then 

 only acid fermentation, which is desirable, takes place. 

 If more air gains entrance, bacteria causing decay will 



FIG. 104. Students constructing a Concrete Silo. (U. S. Dept. of Agriculture.) 



continue the work of the acid-forming bacteria, and 

 rotten silage will result. 



The silo must be deep. Depth is necessary in order 

 to secure pressure on the fodder and thus leave as little 

 air as possible in the mass. From 30 to 40 feet is now 

 recognized as standard depth. 



