276 MICROSCOPICAL JOURNAL. [December, 



Diatoms : Their Life-History and Their Classificatioii. 



By Rev. FRED'K B. CARTER, 



MOUNTCLAIK, N. J. 



[Read before the Essex County Microscopical Society, November 13, 1890,] 



There is no need to plead the cause of the diatoms among micro- 

 scopists. For almost the first word the tyro heard in connection with 

 the microscope was this word " Diatom ;" one of the first slides he ever 

 owned was very likely a slide of diatoms ; the first copy of a Micro- 

 scopic Journal tXvdt he ever saw doubtless had something to say about 

 them. There may be lovers of the tube who are ignorant of rhizopods 

 or desmids, but there are none who don't know anything about diatoms. 

 The difficulty is just the opposite. They think tliey know everything 

 about them, and talk so glibly on the subject that one would suppose 

 they were up in it from A to Z. Anywhere you may hear them dis- 

 cussing learnedly the disputed point as to whether the dots on Angu- 

 lati^in are elevations or depressions, and asserting that they have resolved 

 Saxonica,, or Amphipleura^ or all but resolved it, and yet I venture 

 to say that the majority of amateurs know very little about diatoms, 

 and for this reason : because they have confined their attention to the 

 markings on a few typical forms and those the hardest in the series. 

 The amateur has heard that a good glass of a given power ought to re- 

 solve this or that species, and so he buys a slide and goes to work at it, 

 and if he can't coax his glass to do what he wants he isn't ^satisfied un- 

 til he has gotten hold of one that can ; and then he goes for the next 

 harder form, and so on until he reaches Amphipleura. Till he can re- 

 solve that he is unhappy. And when he has resolved it he spends the 

 rest of his days proudly exhibiting the long-sought objective. As a 

 rule, that satisfies him, and he thinks he knows all there is to be known 

 about diatoms, when as a matter of fact if that is all he knows, he know^s 

 next to nothing about the subject. What he does know and all that he 

 knows is how to show minute dots or resolve fine lines, and a Nobert's 

 ruled band, or a podura scale, or the pygidium of the flea, or the finer 

 tracheal tubes of an insect, would have answered for that. I am 

 tempted to hazard the assertion that there are those who can resolve 

 Amphipleura who can't tell intelligently where it belongs or give any 

 fair description of it, who know scarcely anything about either the 

 structure or arrangement of these forms which are so familiar to their 

 eye. And therefore while it is unnecessary to urge amateurs to observe 

 them it is entirely in order to plead for a wider view of the subject, and 

 to press them to get some definite idea of the principal points connected 

 with their growth and classification. Let me state the questions then 

 which it seems to me the student ought to be able to answer, and do 

 what I can toward supplying the requisite information. 



What is a Diatom ? — It is a plant ; because it can draw its nourish- 

 ment directly from the mineral w^orld, and because its mode of growth 

 allies it to the vegetable rather than the animal kingdom. 



Where in this vegetable kingdom does it belong? — At the very bot- 

 tom of the scale. It ranks with the desmids and below the fungi and 

 lichens. It is a cryptogam, and in the second division of the crypto- 

 gams, the thallogens, and in the very last division of these. That is to 

 say, it belongs to the simplest class of plants that is known, and it is 



