1891.] MICROSCOPICAL JOURNAL. 81 



Diatoms : Their Life History and their Classification. 



By Rev. FRED'K B. CARTER, 



MONTCLAIR, N. J. 



{Continued from f>cige. 6.) 



The article by J. D. Cox on Isthmia Nervosa^ in the Amer. Jotir. 

 of Microscopy for 1S7S, page 97, deserved more careful consideration 

 than could be given to it at the time the second portion of this paper 

 was sent to the printer. As Carpenter has misrepresented Cox, it is 

 only fair that the readers of this Journal should know just what the lat- 

 ter did say in that article. 



"■ Examination fully sustained Dr. WalUch' s stateme/it (italics mine) 

 that the hoop of Isthmia is often found to be of two or more concen- 

 tric tubes, which slide over each other during the multiplication of the 

 diatom by division. * * * The simplest case is that of a diatom 

 with a hoop wide enough for the formation of the new valves. Here 

 the ripened hoop is at least double in thickness ; « « * one thickness 

 of the hoop separates from' the other at one end by a suture of the in- 

 side film, and at the other end by a suture of the outside film, and the 

 two slide over each other till they slide apart. Many cases of this 

 kind have been observed in which the parts of the old hoop are per- 

 sistent, and form the hoop of the new diatom. * * * If we sup- 

 pose that in any species no sutures occur in the hoop, except near the 

 connection between hoop and valve, no cast hoops would be found ex- 

 cept when accident had broken the frustule, for the two lamella would 

 adhere, one to the old and the other to the new valve. * * * Jn 

 regard to Isthmia the cases observed seem conclusively to prove that 

 the hoop proper is a permanent part of the. diatom, except when the 

 separation at the sutures is such as to leave a portion of the hoop free 

 at both edges, in which event the separation of the young frustules 

 drops this segment of the hoop." 



Instead, therefore, of calling in question Walljch's statement, J. D. 

 Cox agrees with Wallich and with H. L. Smith as to the regular for- 

 mation in Isthtnia. Moreover, he does not once use the phrase ' « 

 third hoop' in all that paper. What he says is this: ''The thick 

 band commonly visible in the growing diatom may be caused by the 

 simple lapping of two tubes, but it may also be caused by. a real band 

 (italics inine),the division taking place at its two edges simultane- 

 ously, and the divided inner hoop sliding both ways out of the band, 

 which is loosened and falls when the sepai"ation is complete, giving 

 one of the most common forms in which a perfect cast hoop is found, 

 both margins being smooth and imbi'oken." 



So far then from claiming " a third hoop" as a new discovery. Cox 

 simply affirms his agreement with Wallich's statement and immediately 

 passes on to the real matter of his article, which was intended to eluci- 

 date entirely ditferent points. Carpenter therefore has misrepresented 

 him, and it is a matter of regret to me that I have done anything to per- 

 petuate that unfair criticism. I trust, however, that this explanation 

 may make amends for what was entirely unintentional. I was misled 

 by Carpenter's note. Cox's paper is worthy of close study and should 

 be consulted by every one who is interested in this subject. 



In a former portion of this paper I said that there would always be 



