rupture in their coats adjacent to the aperture. In comparison,
Mackey and Morris (1972a) observed numerous breaks in the spore
coat of C. pasteurianum before the cell emerged through the open
base of the exosporium. An opening in the exosporium, visualised
by TEM, has also been reported in strains of C. pasteurianum
(Mackey and Morris, 1972a) C. botulinum Group I (Stevenson and
Vaughn, 1972), and C. botulinum Group I and C. botulinum Group
II (S. C. Stringer, M. D. Webb, unpublished data).