Catatan

In view of the scope of contributions to this volume on the structure, composition,
and function relating to a range of plant viruses, it is an appropriate time to review the
contribution electron microscopy has made to virology, with special reference to plant
viruses. It is not possible to cover the voluminous literature on the electron microscopy

of plant viruses, but certain landmarks were established which allowed some remark-
able progress to be made up to 1984.

The published work on electron microscopes from 1932 to about 1940 was mainly

concerned with the design and construction of the instrument together with improve-
ments in magnetic and electrostatic lens systems. There were very few reports on ap-
plications to biological specimens, with only a few electron micrographs showing bac-
teria or viruses. It was clear that biological material was relatively transparent to the

electron beam, resulting in very poor contrast causing difficulties in focusing the im-
age. One of the earliest attempts as an aid to focusing was the deposition of colloidal

gold onto the same specimen. The electron micrograph of tobacco mosaic virus (TMV)

taken between 1938/39 using one of the early serially produced Seimens electron mi-
croscopes is an example of this simple technique (see Ruska,' p. 73). Although the

specimen was unstained and without any means of contrast enhancement, slender rods
were faintly visible, with a size range of about 20 nm across and up to several hundred
nanometers long. Among the first attempts to photograph some of the small spherical

viruses (e.g., turnip yellow mosaic virus, TYMV) in the transmission electron micro-
scope, were the experiments reported by Cosslett and Markham' in 1948). Their elec-
tron micrographs of unstained viruses showed small areas of paracrystalline arrays of

the particles when dried down onto thin plastic support films.