ELECTRON :\IICKOSCOPY 



Fig. 9. Direct electron micrograph of a sha- 

 dowed spermatozoid of Fucus serratus; the struc- 

 ture of the proboscis is particularly well shown, 

 X 18,750. {After Manton and Clarke, courtesy of the 

 Annals of Botany) 



structural relationship with broAvn algae. 

 Eleven strands can also be found in ani- 

 mals, for example, Paramoecium (32), the 

 sperms of domestic fowl and fish. The 

 prevalence of the number eleven suggests 

 some fundamental property in the geometric 

 relations of fibres. 



Bacteriology. The electron microscope 

 has been used extensively in the study 

 of bacteria and related organisms. The de- 

 velopment of the thin sectioning technique 

 has permitted bacteria to be sectioned and 

 internal structiu'es to be examined in great 

 detail. In general the study of the surfaces 

 of bacteria using replica techniques is not 

 particularly rewarding, but in a few cases it 

 has been possible to obtain useful informa- 

 tion in this way. The study of bacterial 

 cytology is a complicated and controversial 

 subject which cannot be described in any 



detail here. Much of the controversy arises 

 from interpretations of electron micrographs 

 of thin sections of bacteria. The appearance 

 of sections of bacteria using different types 

 of embedding and staining techniques is 

 always at variance. The recent development 

 of the use of epoxy resins for embedding 

 specimens prior to sectioning (33) has indi- 

 cated that some of the previous work using 

 methacrylate embedding materials is sus- 

 pect. There is no doubt that the wealth of 

 information now available on this subject is 

 becoming much more co-ordinated. 



The use of surface replicas in bacteriology 

 has generally been connected with taxonomic 

 studies such as in the case of the genus 

 Bacillus (34). Here it was shown that the 

 surface sculpturing of spores was different in 

 different species, so that once again the 

 electron microscope proved to be a valuable 

 taxonomic aid. 



Plant Cytology. Plant cytology now 

 covers a wide field. The electron micro- 

 scope has been used in the study of cell walls, 

 mitochondria, chromosomes and other cyto- 

 plasmic inclusions. The specimen techniques 

 required are variable, much of the work 

 being carried out using thin sections, but 

 direct examination and replicas of cell walls 

 have provided much information on their 

 structure. Detailed general reviews of the 

 electron microscopy of the plant cell have 

 been given by Miihlethaler (35) and Buvat 

 (36) and some of the more important findings 

 are described here. 



The Cytoplasm. The structure of the 

 cytoplasm varies according to the fixing 

 agent and may appear as granular or in the 

 form of a fine network. It seems probable 

 that the reticulate structure does not corre- 

 spond to the living state. 



Studies of the distribution of the various 

 albumens and nucleic acids in the cytoplasm 

 have been attempted by forming heavy 

 metal complexes to act as specific electron 

 stains (37), Strugger (38) combined OSO4 

 fixation with uranyl-acetate treatment and 



86 



