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<ul><li><b>Scope and content:</b>  Original caption: Closed propagating cases in the Plant Introduction Greenhouses of the Bureau of Plant Industry at Bell, Maryland. The doors of these cases slide sidewise. Notice the height of the air space in the frames. These are an ideal type of propagating frame for experimental and plant introduction work.</li></ul></div>
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Unknown author<span style="display: none;">Unknown author</span> or not provided</div>
<a href="https://en.wikipedia.org/wiki/U.S._National_Archives_and_Records_Administration" class="extiw" title="en:U.S. National Archives and Records Administration">U.S. National Archives and Records Administration</a>