THE AMERICAN 



MONTHLY 



MICROSCOPICAL JOURNAL. 



Vol. XII. JANUARY, 1891. No. 1. 



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Diatoms: their Life-History and their Classiflcation. 



By Rev. FREDK. B. CARTER, 



MONTCL.\IR, N. J. 



\_Continued from page 280, vol. xt.'\ 



Since the first part of this article was put in print, Wolle's fine work 

 on the Diatomacete of North America has appeared. In Plate I, figs. 

 13, 14, 15 illustrate plainly the point for which I contend. No one 

 can mistake those drawings. And yet even in this magnificent collec- 

 tion of twenty-three himdred figures, the student will find very few 

 besides which indicate clearly the relation of the two valves to each 

 other, not even in the Plate cix of Isthmia. Hei"e, again, the lines of 

 the inner and outer valves are drawn as forming one continuous line. 

 This is the more to be regretted because Isthtnia affords one of the 

 most striking examples of the true I'elation of the valves. Out of the 

 whole 2,300 figures, I can find only ten, exclusive of those just men- 

 tioned, which would lead the student to suspect the true relation, and 

 they might readily be missed among so nnany. (See Plates Ixv, 24 ; 

 Ixxviii, I ; xcv, n ; xcvii, 11 ; xcix, i, 3; cii, 2 ; c, 7, 10, 14.) 



In the same work there is a statement on the structure of the diatoms 

 which strikes us as incorrect. Thus, p. x, we read : '' In the pill-box- 

 like siliceous structure of diatoms, the top and bottom constitute the 

 valves ; the sides are known as the connecti7ig membranes or sutural 

 zones., and when detached are termed hoops. In some the valves do 

 not fold over, but merely rest against each other — edge on edge. The 

 line of junction forms a suture, raphe, or median line, along which the 

 valves readily separate. H. L. Smith divides diatoms into three groups, 

 according to the presence or absence of this suture." 



Here the suture is made identical with the raphe or median line ; 

 whereas, as I understand it, it is entirely distinct. The suture is seen 

 in front view, and is the line of junction of the two valves ; but the 

 raphe or median line is seen in side view, and there is commonly one 



Copyright, 1891, by C. W. Smiley. 



