92 MICROSCOPY FOR BEGINNERS. 



They are difficult to study and to name. To prop- 

 erly examine them demands the highest power object- 

 ives of the best construction, and a skill in the use of 

 the microscope and accessary optical apparatus not at 

 the beginner's command. Much has been written about 

 them, but the literature of the subject is so widely scat- 

 tered through the scientific magazines that only those 

 who make a special study of the diatoms can hope to 

 have it in their libraries. But the beginner need not 

 despair. With ease he can learn to recognize a diatom 

 whenever seen, and to know the names of the com- 

 monest forms, and this is all he will care to learn at 

 first. Yet he will find it a satisfaction to be able to 

 say to a friend, " That is a diatom," and to explain its 

 box-like structure. 



The following Key has been made to assist the be- 

 ginner in ascertaining the names of a few of the com- 

 monest fresh-water forms. It is impossible to include 

 even a tithe of the plants, and the beginner will surely 

 find many not mentioned in the succeeding list, but 

 from the brownish color, the movements common to so 

 many, and the hard, dotted, lined, and sculptured valves, 

 he can readily know them as members of the Diatoma- 

 ceae after he has seen and recognized one. More than 

 this he can scarcely hope to do. 



The brown coloring matter will often be seen con- 

 tracted to a narrow strip or to a spot at each end, and 

 very frequently the frustule will be entirely colorless. 

 Diatoms are the favorite food of many microscopic ani- 



