yi PREFACE 



photographs involving special technic I have sometimes men- 

 tioned the maker and the method used, since every student 

 should learn to make his own photographs and photomicro- 

 graphs if he wishes to excel. Nearly all the photomicrographs 

 were made on the little upright stand (Fig. 55) because I wished 

 to demonstrate to the student that excellent results can be ob- 

 tained with very simple apparatus if one is only willing to take 

 pains. 



The book was written at the earnest request of teachers 

 and by their judgment it will stand or fall. It is the first 

 treatise of its kind in the world and, therefore, I trust, that 

 evidences of crudity will be excused. Not being a teacher, I 

 have been in doubt many times how best to present the difficult 

 subject. 



I shall be glad to receive criticisms and suggestions looking 

 toward a second edition and also notes, photographs, cultures, 

 fresh and dry specimens and separates of papers from all parts 

 of the world, that I may be able to continue my monographic 

 studies. 



ERWIN F. SMITH. 



WASHINGTON, D. C., 

 August, 1920. 



