BRIEF OHNE UMSCHLAG Rossipal, Karl Author: Rossipal, Karl Recipient: Haeckel, Ernst Dating: 14.02.1906
BRIEF [O.A.] Kühnel-Engelsberg, Rudolf Author: Kühnel-Engelsberg, Rudolf Recipient: Haeckel, Ernst Dating: 22.01.1906
BRIEF [O.A.] Lendenfeld, Robert von Author: Lendenfeld, Robert von Recipient: Haeckel, Ernst Dating: 04.10.1906
BRIEF OHNE UMSCHLAG Krauseneck, Gustav Adolf Author: Krauseneck, Gustav Adolf Recipient: Haeckel, Ernst Dating: 01.08.1906