Columbia subject headings:
Poplar--Clones--Middle West.
Poplar--Disease and pest resistance--Middle West.
Poplar--Middle West--Growth.
Poplar--Yields--Middle West.
Harvard subject headings:
Poplar--Clones--Middle West.
Poplar--Disease and pest resistance--Middle West.
Poplar--Middle West--Growth.
Poplar--Yields--Middle West.
Princeton subject headings: