[From the Proceedings of the Boston Society of Natural History, Vol. XL, 
January 8, 1868.] 
NOTE ON A POINT IN THE HABITS OF THE DIA- 
TOMACEiE AND DESMIMACE^J. 
BY ARTHUR MEAD EDWARDS. 
Although most writers on the subject are in the habit of stating 
that many of the genera of Diatomacese in the living state are free, 
or non-adherent to other larger algae or submerged yet 
ahvays 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 existence 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 condition 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 algas, or Tabellarici 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 organ- 
isms 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 Edwards.]. 
362 
[January 8, 
so far as to construct and adopt terms expressing these two condi- 
tions. The adherent forms I grouped under the general head of 
Epiphytaceas and the free under that of Eleutheracean 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 Diatomacese into free and attached genera 
does not exist in nature, and that most, if not all species are free at 
one peri dof 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. Gornphonema acuminatum 
and a Cocconema, the species of which was not at the time determined, 
moved about in a vigorous manner w'hen 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, having its frustules 
free and swimming actively about upon the surface of the water 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 Gornphonema stipes can be found in the same condition. In such 
cases, doubtless, 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 Epiphytacese. 
Once I freed, by violence, Schizonema GreviUei 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, Gomphonem,a and Achnanthes, 
calls up in the mind the question of the individuality of the Diatoma- 
ceasous 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 363 
1868.] 
[Edwards. 
searching investigation. If the whole frond of a Homoeocladia with 
its myriads.of enclosed frustules is an individual, then is the usually 
free Nitzschia, a single frustule of which can , not be morphologically 
distinguished from a single detached frustule of Homoeocladia, also an 
individual? and is a Navicula an individual as well as the group of 
similar forms enclosed within the tube of a Schizonema or the gelat- 
inous frond of a Mastogloia’i Again is a Cyclotella an individual as 
well as the long chain of discs which go to make up the frond of a 
Melosira or Podosira ? Upon this point I shall, hereafter, have more 
to say, merely begging the record of an observed fact bearing thereon 
by students of this extremely interesting, and, I am convinced, import- 
ant branch of natural history. 
I desire to place on record that I have seen at least two, apparently 
and generally acknowledged free species of Desmidiacete, attached to 
a submerged aquatic moss. One was a Closterium, species not deter- 
mined, which was for a long time (as during the most of last summer 
the specimens were growing in one of my aquaria) attached pretty 
firmly, by means of a true stipes or stalk of no great length, to the 
leaves of the moss, and that so strongly that it required some con- 
siderable force to detach it. By rocking the covering glass 
upon the slide, upon which the specimen of moss was placed 
during observation by means of the microscope, the Closterium could 
be made to swing about from side to side upon its stipes without 
becoming detached. The other species, observed at the same time, 
was a Micrasterias, and this was fixed, generally in pairs, to the same 
moss, by its broadest side, or by both valves, so as to present a “front 
view” (as it is termed when speaking of Diatomacese), to the observer, 
thus presenting an analogy to the genus Epithemia of that family 
which occurs growing after the same manner; Cocconeis, on the con- 
trary, is attached by means of the whole of one of the valves. The 
stipes of the Closterium was, of course, at the end of the frustule 
where the valve comes to a point, after the manner of a Cocconema, 
which genus Closterium resembles much in form. In neither of these 
cases do I designate the species, as that I deem hardly of'importance, 
the mere fact of Desmidiacese being found under such conditions 
being the important one. At the same time, it is as well to mention 
that these species were thus found during the month of August, or in 
the midst of the summer, the same forms having been observed free 
and moveable in the early part of the spring. 
I have now to place upon record, my opinion that the Desmidi- 
acea; are governed by very much the same law as applies to their 
apparently near allies the Diatomacete; that is to say, that they are all 
at some period of their existence attached, and at another free.