64 
Note on a Point in the Habits of the Diatomaceje and 
Desmidiaceas. By Arthur Mead Edwards. 
(From the ‘Proceedings of the Boston Society of Natural History,’ vol. xi.) 
Although most writers on tlie subject are in the habit of 
stating that many of the genera of Diatomaceae in the living 
state are free, or non-adherent to other larger algae or sub- 
merged substances, yet always since I first began the study 
of the Protophytes, as is well known to my fellow-students 
with whom I have from time to time discussed the subject, I 
have held that all species are, at some period of their exis- 
tence, in an adherent or attached condition, growing upon, for 
the most part, aquatic vegetation of a larger size. I have 
also frequently expressed the opinion that the adherent con- 
dition of any species was but temporary and conditional ; 
otherwise I could not see how the wide distribution of forms, 
such as Cocconeis scutellum, an extremely widely diffused 
marine species usually found attached to larger algae, or 
Tabellaria flocculosa, an equally cosmopolitan fresh- water 
species found almost invariably attached, was provided for, 
as no motile spores of any kind are known to exist in this 
family, although such may be the case. 
At the outset of my studies of these extremely interesting 
organisms I naturally accepted the classification laid before 
me by the authorities on the subject, and referred the forms 
I found to one or the other of the divisions of free or attached 
genera, and, in fact, went so far as to construct and adopt 
terms expressing these two conditions. The adherent forms I 
grouped under the general head of Epiphytaceae and the free 
under that of Eleutheraceae. 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 facts. At last I have thus to publish my 
conviction that such a division of the Diatomaceae into free 
and attached genera does not exist in nature, and that most 
if not all species are free at one period 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 a similar kind. 
