This collection consists of letters to Yuncker, many requesting determination of Cuscuta and exchange of specimens. Some letters concern his work on the genus for the North American Flora (New York, New York Botanical Garden, 1921); publication of his dissertation, Revision of the North American and West Indian Species of Cuscuta (Urbana, Illinois, University of Illinois, 1921, Illinois Biological Monographs 6[2–3]); and other writings. A very small amount of correspondence relates to Piperaceae. Also included are an 1833 letter from S. S. Weldin of Wheeling, Virginia, to the botanist Jonathan Roberts Paddock (1803–1878) of Worthington, Ohio; two letters from Charles Sprague Sargent (1841–1927) at the Arnold Arboretum, Harvard University, to Wilhelm Miller (1869–1968) in New York, discussing cedars of Lebanon (Cedrus libani A. Richard) and recommending Alfred Rehder (1863–1949) for an Arnold Arboretum department; and handwritten excerpts by an unknown person from published works concerning Cuscuta. See the full list of correspondents and dates of letters in the correspondence inventory.

List of correspondents with dates of letters:

-- Acosta-Solis, Misael (1910–1994): 5 July 1948

-- Agharkar, Shankar Purusottam (1884–1960): 13 February 1923

-- Aitken, M. Winifred (M. W. Betts) (1894–1971): 12 April 1924

-- Allen, Charles Elmer (1872–1954): 31 January 1922, 25 March 1922

-- Aellen, Paul, (1896–1973): 20 November 1933, 15 December 1933, 16 December 1933, 24 February 1934

-- Ames, Oakes (1874–1950): 11 September 1921

-- Anderson, Emma Nathalia (1889–1968): 22 March 1921

-- Anderson, Henry Warren (1885–1971): 30 August 1921

-- H. Aristé-Joseph (Frère) (fl. 1918–1934): 17 January 1920

-- Asplund, Erik, (1888–1974): 20 March 1934

-- Bailey, Liberty Hyde (1858–1954): 28 July 1921, 9 August 1921, 25 January 1923

-- Ball, Carleton Roy (1873–1958): 17 January 1922

-- Barnhart, John Hendley (1871–1949): 1 March 1927

-- Bartlett, Harley Harris (1886–1960): 14 March 1951, 10 April 1951

-- Beauverd, Gustave (1867–1942): 6 April 1926

-- Berry, Edward Wilber (1875–1945): 8 November 1922

-- Bessey, Ernst Athearn (1877–1957): 22 September 1919, 29 September 1919

-- Billington, Cecil (1876–1950): 2 February 1921

-- Bose, Sahay Ram (1888–1970): 25 January 1923

-- Brade, Alexander Curt (1881–1971): 2 August 1949

-- Britton, Nathaniel Lord (1859–1934): 16 August 1919, 5 September 1919, 2 January 1920, 31 January 1920

-- Buchtien, Otto, (1859–1946): 30 December 1919, 8 July 1920

-- Burkill, Isaac Henry (1870–1965): 24 January 1923

-- Burnham, Stewart Henry (1870–1943): 14 January 1922

-- Burns, W.: 22 January 1923, 13 March 1923

-- Cartier, R. D. (fl. 1950s): 22 October 1934

-- Cartwright, Alfred (1950–?): 1 December 1919

-- Cavara, Fridiano (1857–1929): 11 August 1919

-- Chamberlain, Edward Blanchard (1878–1925): 31 October 1921, 10 November 1921

-- Chipp, Thomas Ford (1886–1931): 30 September 1922

-- Chodat, Robert Hippolyte (1865–1934): 6 August ?1915, 20 August 1919, 6 October 1919, 20 October 1919, 13 April 1920, 2 March 1926 (signed by secretary)

-- Clute, Willard Nelson (1869–1950): 24 March 1921

-- Cobb, Collier (1862–1934): 23 May 1919

-- Cook, Melville Thurston (1869–1952): 28 March 1921

-- Coons, George Herbert, (1885–1980): 22 April 1931

-- Costello, David Francis (1904–1990): 30 October 1931

-- Coulter, Stanley (1853–1943): 17 March 1921

-- Croizat, León Camille Marius (1894–1982): 17 May 1948

-- Cuatrecasas, Arumi José, (1903–1996): 7 June 1948

-- Darlington, Henry Townsend (1875–1964): 7 February 1921, 18 March 1921

-- Deam, Charles Clemon (1865–1953): 9 December 1919, 21 December 1919, 11 November 1920, 8 October 1930, 21 June 1932, 23 August 1933

-- Dean, Henry Lee (1907–1986): 30 October 1929, 7 April 1934, 29 October 1934

-- Debbarman, Peary Mohon (1887–1925): 16 April 1923, 11 July 1923

-- Degener, Otto, (1899–1988): 26 May 1925

-- Demaree, Delzie (1889–1987): 14 March 1932

-- Diels, Friedrich Ludwig Emil (1874–1945): 10 May 1926

-- Dudgeon, Winfield Scott (1886–1932): 25 March 1919, 16 March 1923

-- Dugand, Armando (1906–1971): 17 May 1948

-- Eastwood, Alice (1859–1953): 4 June 1919, 9 May 1921

-- Engler, Heinrich Gustav Adolf (1844–1930): 21 June 1925

-- Evans, Alexander William (1868–1959): 20 January 1922, 9 March 1922

-- Farwell, Oliver Atkins (1867–1944): 1 December 1920

-- Fedtschenko, Boris Alexeievitsch (1872–1947): 23 December 1925, 15 January 1926, 13 December 1926

-- Ferguson, William Cashman (1861–1930): 30 October 1924, 27 October 1929

-- Fitzpatrick, Thomas Jefferson (1868–1952): 14 March 1921

-- Gager, Charles Stuart (1872–1943): 5 April 1921

-- Gagnepain, François (1866–1952): 19 December 1926

-- Gates, Frank Caleb (1887–1955): 28 May 1921

-- Gleason, Henry Allan, (1882–1975): 15 September 1919, 6 November 1929, 13 January 1930

-- Graves, Arthur Harmount (1879–1962): 16 December 1922

-- Greenman, Jesse More (1867–1951): 29 March 1921, 7 August 1924

-- Gundersen, Alfred Ludvig Georg (1877–1958): 13 July 1921, 14 November 1922, 22 November 1923

-- Hall, Harvey Monroe (1874–1932): 13 August 1922

-- Hansen, Albert August (1891–1940): 21 March 1922

-- Harper, Roland McMillan (1878–1966): 2 December 1941

-- Harris, James Arthur (1880–1930): 27 December 1924, 14 October 1925

-- Hazen, Tracy Elliot (1874–1943): 13 March 1929, 2 August 1930, 20 July 1931, 23 October 1931, 3 April 1932, 28 May 1932 (letter and telegram)

-- Heimlich, Louis Frederick (1890–1928): 20 April 1923

-- Herter, Wilhelm Gustav (1884–1958): 2 October 1933, 2 February 1952

-- Hill, Arthur William (1875–1941): 4 February 1926, 8 March 1926

-- Hoehne, Frederico Carlos (1882–1959): 19 July 1921, 28 November 1921, 21 January 1931, 16 June 1932, 10 November 1933

-- Holman, Richard Morris (1886–1935): 6 October 1919, 29 October 1919

-- Holmgren, Ivar Albert (1889–1975): 11 December 1920

-- Holway, Edward Willet Dorland (1853–1923): 21 January 1922, 6 February 1922, 31 March 1922

-- House, Homer Doliver (1878–1949): 11 February 1922, 16 February 1922

-- Hunziker, Armando Teodoro, (1919–2001): 10 September 1945

-- Hürlimann, Hans (1921–2014): 25 May 1952

-- Jennings, Otto Emery (1877–1964): 26 March 1921

-- Jepson, Willis Linn (1867–1946): 8 January 1920

-- Just, Theodor Karl (1904–1960): 14 April 1932

-- Kamensky, K. (fl. 1915–1932): 2 February 1932, 17 July 1932, 3 October 1932

-- Kashyap, Shiv Ram (1882–1934): 1923

-- Kerr, Arthur Francis George (1877–1942): 21 April 1923

-- Killip, Ellsworth Paine (1890–1968): 12 February 1931, 9 October 1933, 7 November 1933

-- Kossenko, Ivan Sergeevich (1896–?1976): 16 December 1933

-- Laidlaw, William (ca. 1866–1925): 5 February 1923, 23 May 1923

-- Lecomte, Paul Henri (1856–1934): 7 June 1921, 9 March 1926, 11 December 1926

-- Lemée, Albert Marie Victor (1872–1961): 3 August 1952

-- Lindman, Carl Axel Magnus (1856–1928): 24 May 1921, 24 November 1921, 21 April 1923

-- Litardière, René de (1888–1957): 19 May 1952

-- Looser, Gualterio (1898–1982): 16 March 1931, 4 May 1931, 30 May 1931, 24 December 1931, 22 February 1932, 1 March 1932

-- Lowe, John N. (?–1938): 21 February 1921

-- MacKenzie, Kenneth Kent (1877–1934): 15 March 1921, 22 March 1921

-- Maiden, Joseph Henry (1859–1925): 23 May 1923

-- Maxon, William Ralph (1877–1948): 3 November 1933, 5 December 1933, 17 May 1934

-- McWhorter, Frank Paden, (1896–1985): 23 March 1926

-- Merrill, Elmer Drew (1876–1956): 31 May 1923, 9 March 1925, 2 December 1925, 5 March 1930, 24 December 1931, 8 January 1932, 19 January 1932, 6 June 1932, 12 July 1932

-- Meyer, Teodoro (1910–1972): 3 March 1953

-- Millspaugh, Charles Frederick (1854–1923): 5 March 1923, 16 March 1923

-- Moldenke, Harold Norman (1909–1996): 20 September 1933, 4 October 1933

-- Muenscher, Walter Conrad Leopold (1891–1963): 12 February 1932, 2 January 1934

-- Munerati, Ottavio (1875–1949): 24 October 1931, 2 February 1932, 14 March 1932, 8 February 1934

-- Munz, Philip Alexander (1892–1974): 28 March 1931

-- Nelson, Aven (1859–1952): 8 May 1919

-- Nelson, James Carleton (1867–1944): 17 July 1927, 29 July 1922

-- O’Donell, Carlos Alberto (1912–1954): 27 April 1953

-- Oliver, Walter Reginald Brook (1883–1957): 24 November 1925

-- Osborn, T. G. B.; Osborn, Theodore George Bentley (1887–1973): 27 June 1923, 13 March 1923

-- Palibin, Ivan Vladimirovic (1872–1949): 7 February 1926

-- Pammel, Louis Hermann (1862–1931): 27 January 1922

-- Parham, Bayard Eugene Vincent (1902–1987): 31 December 1951

-- Parodi, Lorenzo Raimundo (1895–1966): 14 February 1930, 22 May 1930, 26 October 1930, 7 July 1931, 31 October 1931, 20 August 1933, 3 November 1933

-- Patwardhan, G. B. (fl. 1920–1930): 8 June 1926

-- Payson, Edwin Blake (1893–1927): 28 March 1922

-- Pearl, Raymond (1879–1940): 8 January 1929

-- Peattie, Donald Culross (1898–1964): 12 January 1924

-- Peglion, Vittorio (1873–1967): 17 January 1922

-- Peirce, George James (1868–1954): 19 January 1920

-- Peiterson, Arne Kristopher (1884–1924): 16 January 1922

-- Pennell, Francis Whittier (1886–1952): 4 April 1921, 27 April 1921, 25 March 1931, 16 April 1931

-- Pilger, Robert (1876–1953): 30 February 1922

-- Pittier, Henri François (1857–1950): 26 July 1923

-- Ponce de Léon, Antonio (1887–1961): 2 June 1951

-- Pool, Raymond John (1882–1967): 21 March 1921

-- Prain, David (1857–1944): 25 September 1920, 13 April 1921, 26 May 1921

-- Pulle, August Adriaan (1878–1955): 25 May 1920

-- Rambo, Balduino (Brother): (1906–1961): 6 June 1948

-- Ramírez Cantú, Débora, (1919–, fl. 1943–1953): 29 February 1952

-- Rankin, Walter Mead (1857–1947): 27 April 1921, 11 May 1921

-- Rauh, Werner (1913–2000): 8 February 1855

-- Ravenel, William de Chastignier (1859–1933): 20 October 1924

-- Rechinger, Karl Heinz (1906–1998): 15 November 1951, 26 September 195?

-- Reitz, Prêmio Raulino (1919–1990): 5 October 1950

-- Robinson, Benjamin Lincoln (1864–1935): 23 March 1921, 29 March 1921, 9 April 1921, 14 June 1921, 21 June 1921, 29 June 1921, 4 November 1921, 15 September 1924, 24 September 1924

-- Rodway, James (1848–1926): 4 September 1919

-- Rose, Joseph Nelson (1862–1928): 28 July 1919, 17 February 1920, 19 March 1921, 19 September 1922

-- Rosendahl, Carl Otto (1875–1956): 6 October 1933, 13 October 1933

-- Rydberg, Per Axel (1860–1931): 19 April 1917

-- St. John, Harold (1892–1991): 6 November 1925

-- Salisbury, (Sir) Edward James (1886–1978): 11 March 1952, 14 March 1952

-- Samuelsson, Gunnar (1885–1944): 9 February 1934

-- Sargent, Charles Sprague (1841–1927): 31 October 1908, 12 October 1909 (to Wilhelm Miller, New York)

-- Saxton, Walter Theodore (1882–1973): 22 February 1923

-- Schinz, Hans (1858–1941): 27 August 1919, 3 September 1919, 19 September 1919, 14 October 1919, 16 October 1919, 13 February 1920

-- Schlecter, Franz Richard Rudolf (1872–1925): 30 March 1920, 27 June 1920, 15 December 1920, 14 February 1921, 20 June 1921

-- Schönland, Selmar (1860–1940): 6 February 1923

-- Scolnik, Rosa (1906–1979): 20 May 1951

-- Setchell, William Albert (1864–1943): 20 April 1923, 8 May 1923, 26 February 1923, 23 September 1930

-- Seymour, Arthur Bliss (1859–1933): 20 June 1919

-- Tharp, Benjamin Carroll (1885–1864): 16 January 1923

-- Skeels, Homer Collar (1873–1934): 26 October 1922

-- Skottsberg, Carl Johan Fredrik (1880–1963): 14 October 1951

-- Small, John Kunkel (1869–1938): 11 July 1921, 5 December 1929

-- Smiley, Frank Jason, (1880–1969): 20 May 1919, 10 June 1919

-- Emilie Snethlage (1868–1929): 29 January 1920

-- Standley, Paul Carpenter (1884–1963): 2 November 1920

-- Stahel, Gerold (1887–1955): 29 Jun 1887

-- Stehlé, Henri (1909–1983): 25 December 1945

-- Stevens, Orin Alva (1885–1979): 3 June 1919, 17 March 1921

-- Stewart, Ralph Randles (1890–1993): 28 July 1923

-- Stout, Gilbert Leonidas (1898–1963): 9 May 1934, 5 June 1934, 19 June 1934

-- Taubenhaus, Jacob Joseph (1884–1937): n.d.

-- Taylor, George (1904–1993): 17 November 1950

-- Tehon, Leo Roy (1895–1954): 7 March 1931

-- Thornber, John James (1872–1962): 28 April 1919

-- Traverso, Giovanni Battista (1878–1955): 20 September 1922, 9 May 1922

-- Trelease, William (1857–1945): 20 October 1919, 23 March 1921, 14 December 1921, 15 December 1921, 10 February 1922, 2 March 1926, 22 May 1931, 11 May 1934

-- Urban, Ignatius (1848–1931): 11 January 1930

-- Verdcourt, Bernard (1925–2011): 20 March 1951

-- Walker, Elda Rema (1877–1971): 10 January 1921, 18 March 1921

-- Wall, Arnold (1869–1966): 1 November 1924

-- Weatherby, Charles Alfred (1875–1949): 22 January 1922

-- Weldin, S. S.: 5 May 1833 (to J. R. Paddock)

-- Wheeler, Louis Cutter (1910–1980): 8 December 1934

-- Wilson, Percy (1879–1944): 15 March 1926, 30 January 1930, 25 March 1932

-- Wolff, Simon Emanuel (1892–1980): 25 September 1931, 1 June 1932