ELECTRON MICROSCOPY 



Fig. 16. Pit membrane in a simple pit in the radicle of maize, X 15,000. (After Milhlethaler, 

 courtesy of Die Naturwissenschaften) 



It is possible to study changes in the pri- 

 mary cell wall structure during cell division. 

 The manner in which the cellulose micro- 

 fibrils are deposited can be examined. The 

 secondary cell wall contains characteristic 

 perforations known as pits. These pits have 

 been studied extensively in the electron 

 microscope and whereas optical evidence 

 suggested that the pit membrane, which 

 stretches across the perforation, acts as an 

 impassable barrier, the electron microscope 

 indicates that it is porous in nature (Figure 

 16). 



Cell wall growth has been studied in detail 

 in the onion root tip by Scott et al. (40). 



Conclusion. The electron microscope is 

 clearly very valuable in botanical research. 

 It is extremely useful as a taxonomic aid, 

 and much morphological information has 

 been obtained in the field of plant cytology. 

 It remains for these results to be correlated 

 with biochemical investigations. 



Acknoivledgments. The author would like to 

 thank the following for material and advice: 

 Professor and Mrs. T. M. Harris, University of 

 Reading; Dr. K. Miihlethaler, Eidgenossische 

 Technische Hochschule, Zurich; and Dr. B. E. 

 Juniper, University of Oxford; also Dr. T. E. 

 Allibone, F.R.S., Director of the Research Lab- 

 oratory, for permission to publish this article. 



REFERENCES 



1. Fernandez-Moran, H. and Dahl, A. O., 



Science (Lancaster, Pa.) 116, 465 (1952). 



2. MiJHLETHALER, K., Mikroskopie, 8, 103 (1953). 



3. Afzelius, B. M., Erdtman, G., and Sjos- 



TRAND, F. S., Sv. Bat. Tidskr., 48, 155 (1954). 



4. Afzelius, B. M., Grana Palynologica, 1, 22 



(1956). 



5. MtJHLETHALER, K., Platita, 46, 1 (1955). 



6. Bradley, D. E., Brit. J. Appl. Phys., 5, 96 



(1954). 



7. Bradley, D. E., New Phytol., 57, 226 (1958). 



8. Rowley, J. R., Grana Palynologica, 2, 3 



(1959). 



9. Bradley, D. E., Mikroskopie, 13, 180 (1958). 



10. Gregory, P. H. and Nixon, H. L., Trans. 



Brit. Mycol. Soc. 33, 359 (1950). 



11. Agar, H. D. and Douglas, H. C., J. Bac- 



teriol., 70, 427 (1955). 



12. Bradley, D. E., J. Roy. Micros. Soc, 75, 254 



(1956). 



13. MtJLLER, H. O. AND Pasewaldt, C. W. a., 



Natunviss., 30 (1942). 



14. KoLBE, R. W. AND GoLZ, E., Ber. dtsch. hot. 



Ges., 61, 91 (1943). 



15. HusTEDT, F., Arch, hydrobiol. Plankt., 41, 315 



(1945). 



16. Hendey, N. I., Gushing, D. H. and Ripley, 



G. W., /. Roy. Micros. Soc, 74, 22 (1954). 



17. Halldal, p. and Markali, J., Avhandlinger 



Utgitt av Det Norske Videnskeps-Akademi, 

 Oslo. Mat-Natruv. Klasse, No. 1 (1955). 



18. Bradley, D. E., J. Appl. Phys., 27, 1399 



(1956). 



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