EDUCATIONAL VALUE OF PHOTOMICROGRAPHY. 153 



esting details about seeds, leaf structure, etc. It is quite possible that 

 the microscope may yet serve to answer the present disputed question as 

 to how the water can rise into the tops of the great trees of California, 

 some of which are over 300 feet from the ground. It may also be men- 

 tioned that photomicrographs are 

 of much importance in studying 

 insects and parasites that infest 

 and destroy forest and fruit trees. 

 In fact, the preservation or anni- 

 hilation, as seems best to serve 

 man's purpose, of certain organ- 

 isms is determined very largely 

 by the revelations of the micro- 

 scope. When such a thing as the 

 lack of assimilating power of a 

 leaf due to insufficient amount of 

 light may be shown by a photo- 

 graph, the far-reaching value of 

 this science can be understood. 



Its intimate connection with 

 botany and plant structure in gen- 

 eral is in fact so well recognized 

 as to need little comment here. 

 Some work in connection with 

 cotton fibers, however, is interest- 

 ing as it shows how it is possible 

 to detect injury to the fiber in the 

 process of ginning; such photo- 

 graphs in connection with others 

 of like character, render valuable 

 information concerning textile 

 materials (Fig. 12). 



In crystallography the photo- 

 micrograph is useful. Figs. 13-18 

 illustrate the appearance in polar- 

 ized light of a few crystals of both 

 organic and inorganic substances. 

 Perhaps one of the richest of all 

 substances in variety of form of crystals is snow. 'While the geometrical 

 form is invariably hexagonal, it occurs in countless combinations and 

 many of the crystals are very beautiful. For procuring pictures of snow 

 crystals it seems necessary to use the apparatus in a temperature below 

 the freezing point. The snow crystals are collected as they fall upon 

 a surface too cold to tend to melt them, and if the work is done quickly, 



Fig. 19. Snow Crystals. 



