BOTANICAL APPLICATIONS 



ment of the pollen grain of Tradescantia 

 pahidosa. It is of considerable interest that 

 he found that the basic form of exine sculp- 

 turing orginated very early in development. 

 The intine was not recognizable until much 

 later. 



The entire structure of the sporoderm, 

 both internal and external, can be full}^ 

 elucidated by the judicious employment of 

 replicas and thin sections. 



Moss Spores. The spores of mosses and 

 similar plants present a similar problem in 

 replication and sectioning to pollen grains. 

 Afzelius, Erdtman and Sjostrand (3) have 

 studied the fine structure of the outer part 

 of the spore wall of Lycopodium davatum 

 using thin sections, the results indicating 

 that the spore wall is divided into two layers, 

 the outer being laminated and the inner 

 granulated. 



Moss spores have not been studied ex- 

 tensively, the only example being by Bradley 

 (9), who shows electron micrographs of the 

 surface structure of spores of Atrichum undu- 

 latum and Dicranella heteromalla. It seems 

 that the value of studying such specimens 

 in the electron microscope is somewhat 

 limited. 



Fungi. The direct examination of fungus 

 spores of a number of different species was 

 carried out by Gregory and Nixon (10). The 

 spore structure is of interest in studies of 

 asthma as is the case with pollen grains. 

 Direct electron micrographs only provide a 

 silhouette of the spores and little can be seen 

 of their surface structure; the use of replicas, 

 however, shows the surface structure clearly 

 as in Figure 5. 



An interesting application of the electron 

 microscope using both surface replicas and 

 sections has been carried out independently 

 by two authors on the division of Saccharo- 

 myces cerevisiae (11, 12). The morphology of 

 the different types of yeast bud scars and 

 the mechanism of the division process was 

 studied by replicas in the case of Bradley 

 (12) and sections in the case of Agar and 



Douglas (11), both authors independently 

 reaching similar conclusions. 



Algae. A group of algae which has been 

 studied extensively in the electron micro- 

 scope is that comprising the diatoms. So 

 much work has been carried out that it is 

 impossible to include more than a brief ref- 

 erence. Much of the work was done in the 

 earh^ days of electron microscopj^ and sev- 

 eral important contributions were made by 

 MuUer and Pasewaldt (13), Kolbe and Golz 

 (14), Hustedt (15), and Hendey, Cushing 

 and Ripley (16). The electron microscope is 

 continually being used, generally as a tax- 

 onomic aid in studies of new species or popu- 

 lations. 



The light microscope is fully adequate for 

 distinguishing the diatom genera, and also 

 for separating the great majority of species. 

 However, the electron microscope permits a 

 much fuller examination of the submicro- 

 scopic details of the silica valve and thus 

 enables a far better understanding of the 

 meaning of its finer visible features to be 

 achie^'ed. In addition, the hope is that it will 

 provide useful information about the de- 

 velopment of this fine structure. 



The electron microscope has also been 

 used in the study of one family and three 

 genera of algae belonging to the Chryso- 



FiG. 5. Shadowed carbon replica of a spore of 

 the fungus Russula mairei, X9000. 



83 



