“…The occlusion of the conducting vessels of ulmi-infected elm by tyloses has been similarly observed (Schwarz, 1922;Wollenweber, 1929;Broekhuizen, 1929;Buisman, 1933;Clinton and McCormick, 1936;Kerling, 1955;Beckman, 1958;Ouellette, 1962;Wilson, 1965;Tchernoff, 1965). Schwarz (1922) stated that the first changes in appearance of infected elm wood were in the form of what she calls "bladder-like thylloses"…”