1870.] 195 [Stodder. 



Maynard of Newtonville, Mr.' Frank H. Nutter of W. Rox- 

 bmy, and Messrs. George F. Child, A. A. Childs, D. M. Fisk, 

 Emile Fontarive, Robert A. Shailer, Hollis Thayer, John H. 

 Thorndike and William F. Whitney of Boston, were elected 

 Resident Members. 



Section of Microscopy. January 12, 1870. 

 Mr. R. C. Greenleaf in the chair. Eight members present. 



Mr. Stodder referred to a communication of Mr. R. C. 

 Greenleaf, 1 on a specimen of Aulacodiscus oreganus Bail., 

 prepared by Mr. Samuels, which in the process of mounting 

 separated into two plates ; one being the outer, and the 

 other the inner plate of one valve. 



A few days since a similar thing happened to Mr. Samuels when 

 mounting another specimen of the same species. The Diatom sepa- 

 rated into two pieces, the inner and outer plates of one valve, as Mr. 

 Samuels supposed. But a careful inspection of the specimen, which 

 was exhibited to the Section, indicated an entirely different origin. 

 One disc was a perfect A. oreganus, with all the characters of that 

 species, having ten rays, and " feet." The other was more hyaline, 

 the umbilicus less distinct, the granules and "feet " imperfectly devel- 

 oped, and had eleven rays and " feet." Mr. Stodder's explanation 

 of the appearances — if Mr. Samuels was not mistaken as to the facts 

 — is that one disc is the parent, and the other a valve of a new 

 frustule, which was forming in the process of self-division, the growth 

 of which was stopped before it had come to maturity. Ehrenberg 

 and some other naturalists have made the number of rays in such 

 forms a specific character; Bailey and others have rejected this prin- 

 ciple of classification, but here for the first time we have positive 

 evidence that a form with eleven rays has been derived directly from 

 one of ten rays. Such a change of characters in one order of plants 

 being authentically established, it is a reasonable inference that all 

 other orders mav be liable to similar changes, and therefore great 

 caution should be used in allowing specific value to unimportant 

 characters. 



i These Proceedings, Vol. xn, p. 361. 



