SUMMARY Images of filamentous and unicellular algae have been obtained by soft X‐ray (wavelength 2.05‐4.4 nm) contact microscopy (SXCM), using synchrotron radiation, and the images obtained compared to those obtained by scanning and transmission electron microscopy. After chemical development to leave areas corresponding to high X‐ray absorbance by the specimen the photoresists were examined by SEM. In two algae (Anabaena and Trebouxia) cytoplasmic detail, including photosynthetic lamellae, chloroplasts, nuclei and mitochondria, were identified. In a third alga (Cyanidium) the SXCM image revealed little internal detail due to the uniformly high X‐ray absorption by the cells. The successful imaging of whole cells by SXCM is discussed in relation to conventional TEM and the future possibilities for SXCM are outlined.

The optical properties of a confocal scanning microscope that was designed to utilize a synchrotron as light source are presented. The usable spectral range is from 200 nm up to 700 nm. Using 325-nm laser light, it is shown that the lateral resolution is about 125 nm, and the axial resolution better than 250 nm. After transport of the microscope from Utrecht to the Daresbury Synchrotron Source, 200-nm excitation can be applied, and the lateral resolution will drop to below 100 nm.

Soft X-ray ( 2 4 5 4 . 4 nm) contact microscopy, using synchrotron radiation, of ultrasections of lead-polluted chloragogenous tissue of the earthworm Dendrobaena rubida has been achieved. The positive resist, after etching to leave areas corresponding to high absorbance in the tissue, is viewed by SEM and the imaging compared with the same section viewed, after irradiation, by TEM. No radiation damage ..JS evident and the lead deposits associated with the chloragosomes and within the debris vesicles imaged clearly. The characteristics of the broad beam have thus produced a lead 'map'. Resolution is in the order of 70nm. The results are compared with the markedly different imaging of control tissue containing insignificant lead levels.

No abstract

Contact images (CI) of dehydrated, nucleolar chromatin from amphibian oocytes have been produced by soft X-rays from a synchrotron radiation source. These CI have been compared with the morphology of the original chromatin as seen in scanning and transmission electron microscopes. The quality and informational content of the CI depend very much on certain preparative procedures. The following factors have a marked effect on image quality and need to be carefully controlled: the total X-ray dose, the time and nature of development and the distance of the specimen from the photoresist. The preparation of the chromatin itself, providing that it is critically point dried, is less important. By following a regime of high X-ray dose, sufficient for penetration of the rather thick chromatin rings, and gentle development so that fine detail is not dissolved from the resist surface, it has been possible to obtain images dhich closely resemble the original chromatin, although the detailed resolution of the CI is not as clear. The smallest biological structures clearly resolved in the CI are ribonucleoprotein granules, which vary in size from 200 to 800 nm. However, by further refinement ofpreparative conditions it should be possible to improve on the informational content of these images.