ELECTRON MICKOSCOI'V 



Fig. 5. Adaxial leaf surface of Pisum satium 

 var. 'Alaska'. Grown at 1500 ft. candles light in- 

 tensity. 



Fig. 6. Adaxial leaf surface of Pisum sativum 

 var. 'Alaska'. Immediately after transfer from 

 darkness to light. 



Treating the soil in which peas are germi- 

 nating with 2,2-dichlorpropionic acid ("Dal- 

 apon") affects the susceptibihty of the pea 

 plants subsequently sprayed with certain 

 herbicides (Dewey, Gregory and Pfeiffer, 

 1956). It was thought that the "Dalapon" 

 interfered with the wax formation of the 

 cuticle and so enhanced the retention and 



penetnition of the lu'ri)icides. The electron 

 microscope shows that there is a progressive 

 reduction in the complexity, size, and density 

 of the wax projections on the pea leaf sur- 

 faces W'ith increasing concentration of 

 "Dalapon" in the soil. Increases in the con- 

 centration of "Dalapon" in the soil beyond 

 0.32 lb per acre finally result in a smooth 

 cuticle with no w^ax projections visible at all 

 (Juniper, 1959). 



The initial development of the fine struc- 

 ture of a leaf is shown by the electron micro- 

 scope to take place before the earliest stage 

 at which replicas can be made. The stages 

 of the development of the fine structure of a 

 pea leaf surface have therefore been followed 

 by growing the pea plant to an advanced 

 stage in darkness (during which time no pro- 

 jections are developed) and then transferring 

 it to light. Replicas are then taken of corre- 

 sponding leaves at 24 hour intervals. The 

 projections from the surface develop very 

 rapidly. Figure 6 is of a pea leaf surface im- 

 mediately after transfer. The appearance of 

 Fig. 4 is achieved after about five days. 



New techniques and the electron micro- 

 scope have revealed the existence of a fine 

 structure on the surfaces of many plants 

 which had never previously been suspected. 

 Oiu' investigations have confirmed some of 

 the observations made by other workers 

 using different techniques in the same field. 

 It has revealed morphological differences re- 

 sulting from en\'ironmental changes which 

 were not previously suspected because the 

 techniciues for detecting such changes in the 

 fine structure were not sufficiently refined. 

 The results are interesting both to the de- 

 velopmental morphologist and to the agrono- 

 mist because the view that everything 

 external to the epidermal cells is static and 

 immutable can, with present evidence, no 

 longer be held. 



REFERENCES 



Bradley, D. E., "Evaporated carbon films for 

 use in electron microscopy," Brit. J. Appl. 

 Phys., 5, 65 (1954). 



Bradley, D. E., "High-resolution shadow-casting 



180 



