ELECTRON MICROSCOPY 



scope compared with the Ught microscope in 

 the study of pollen grains have been discussed 

 by Bradley (7). For example, when studying 

 pores, their outline can generally just be 

 distinguished in the light microscope. With 

 the electron microscope, however, the entire 

 morphology is clearly resolved. A comparison 

 between the pores of Plantago media and 

 Plantago lanceolata is shown here. The pore 

 of P. media (Figure 3) has a ragged outline 

 and contains a number of irregularly scat- 

 tered large protrusions; that of I\ lanceolata 

 is circular and completely different in form. 

 This difference can just be detected in the 

 light microscope, but the true structures 

 cannot be resolved. 



Surface replicas have indicated that the 

 effect of the acetolyzation process on the 

 sub-microscopic structure of the pollen grain 

 surface is negligible. It might be expected 

 that the use of powerful reagents such as 

 those employed in acetolyzation would pro- 

 duce artefacts in the sporoderm. This is not 

 the case with pollen grains studied in the 

 light microscope and there appears to be no 



Fig. 3. Shadowed carbon replica of a fresh pol- 

 len grain of Plantago media, X9000. (Courtesy of 

 the New Phytologist) 



Fig. 4. Shadowed carbon replica of a fresh pol- 

 len grain of Plantago lanceolata, X9000. (Courtesy 

 of the New Phytologist) 



noticeable effect at electron microscope levels 

 of resolution. 



An important problem in the study of pol- 

 len grains is the distinction between ap- 

 parently identical grains of different species. 

 If a separation of these species could be ob- 

 tained it would be of considerable value in 

 quaternary research. Preliminary electron 

 microscope studies of Cannabis and Humu- 

 lus, Coryhis and Myrica have not produced 

 the distinction hoped for. In the former case 

 Cannabis and Humulus appeared identical 

 in the electron microscope with regard to 

 their surface structures. However some slight 

 but definite structural distinction was found 

 between Coi'ylvs and Myrica grains. 



Rowley (8) has used both sectioning and 

 surface replicas in an exhaustive study of the 

 pollen wall in eleven species in the Com- 

 melinaceae. No basic differences were found 

 in the structural elements making up the 

 mature pollen wall; morphological ^•aria- 

 tion at light microscope level was due to 

 variations in the arrangement of these 

 elements. Rowley also studied the develop- 



82 



