A CRITICAL-EXAMINATION OF SEM ULTRASTRUCTURAL FEATURES IN 2 PENICILLIUM-THOMII ISOLATES FROM SOIL

A SEM ultrastructural study of two isolates of a soil fungus, Penicill ium thomii, is presented, which compares the morphology of critical po int-dried tissues with cryofixed material. The paper also reports feat ures of the isolates which sometimes are different from the usual diag nostic morphological data for this fungus. Thus, branched penicilli ha ve been seen in one of the isolates on MEA, yet monoverticillate penic illi are regarded as a major feature of P. thomii. In the same isolate the stipes appear non-vesiculate on both agars unlike the vesiculate stipes normally associated with this species from light microscope obs ervations. Some wrinkling is seen in the stipes and phialides from cri tical point-dried specimens and this phenomenon is generally absent in cryofixed samples, although in one isolate, collapse of some of the p hialides occurred. Critical point-drying results in shrinkage of conid ia. Penicillium thomii is an important species in soil ecosystems and thus an accurate description of its morphological features is desirabl e for proper classification although it is a widely held belief that n o character in Penicillium taxonomy is totally invariant.