Sentence:  It is sometimes necessary to provide storage for grain beyond the normal capacity of an elevator facility or elsewhere. In such conditions a relatively inexpensive expedient is the <WSD>flat store</WSD>. This is little more than a cover for a pile of dry grain adopting its natural form as poured. 
Meaning of the word marked with <WSD> tags:  A storage facility in which the material stored is simply piled on a floor (as opposed to a bin or silo).