Edwards.] 362 [January 8, 



SO ftir as to construct and adopt terms expressing tliese two condi- 

 tions. The adherent forms I groujjed under the general liead of 

 Epiphytaceae and the free under that of Eleuthei-acese. As my 

 studies progressed, however, I was continually meeting with cases in 

 which this arbitrary mode of division would not apply, and the natural 

 conclusion come to was that the method was defective, as it did not 

 agree with tacts. At last I have thus to publish my conviction that 

 such a division of the Diatomaceaj into free and attached genera 

 does not exist in nature, and that most, if not all species are free at 

 one peri d of their existence and attached at another. I have seen 

 several species which are almost universally ranked as fixed species 

 existing in a natural state free and possessed of motion which they 

 never displayed in their attached condition. Although it is not my 

 intention at the present time to go very deeply into this subject, yet 

 I desire to record that I have noted the following instances of such 

 occurrences among others of similar kind. Gomplionema acuminatum 

 and a Cocconemn, the species of which was not at the time determined, 

 moved about in a vigorous manner Avhen found naturally detached 

 and also when freed from their stipes by violence. Again, several 

 years ago I made a gathering of Schizonema cruciger, a species which 

 consists of siliceous frustules enclosed within tubes of membranous 

 material growing upon other submerged matter, ha^'ing its frustules 

 free and swimming actively about upon the surflxce of the Avater with- 

 out any signs of investing tubes, which, however, were found empty 

 but standing erect and adherent at the bottom of the ditch inhabited 

 by the Schizonema. I have noticed that bare stipes of an Achnan- 

 thes, without any pendent frustules, are by no means uncommon, and 

 also Gomphontiiia stipes can be found in the same condition. In such 

 cases, tloubtless, the freed frustules might be found near by, and, in 

 fact, I have in what may be called '"free" gatherings, floating upon the 

 surface of the water, observed Cocconeis, Achnanthes, and other forms 

 which, at one time I was in the habit of classifying as Epiphytaceae. 

 Once I freed, by violence, Schizonema GreoiUei and a Synedra which 

 accompanied it, and they both moved about in a rather lively manner, 

 although the motion of the Schizonema was much more vigorous than 

 that of the Synedra. This was not remarkable, as the frustules of 

 Schizonema and Homceocladia are well known to be freely moveable 

 within their investing tubes, although I do not remember to have seen 

 the fact of their activity without that enclosure recorded. The 

 observance of these facts of the motion of the detached frustules of 

 such well-known forms as Schizonema., Gomplionema and Achnanthes, 

 calls up in the mind the question of the individuality of the Dlatoma- 

 ceaeous frustule, and it is a point to which I would call the attention 

 of students as one deserving and, in fact, calling for further and 



