WHAT IS A DESMID? 315 

of observation. Many if not all of the Desmids, it is true, 
possess the extraordinary power of slowly changing their 
place, so that in time, varying with the particular forms ob- 
served, they approach the side of the bottle in which they 
are enclosed, upon which the most light shines, and not only. 
so, but many appear to have a contia but steady progres-" 
sive mode of motion, as when viewed by means of the mi- 
croscope they are observed to traverse the field of view 
under the eye of the observer. Yet it cannot be said that 
this faculty allies them to animals, for not only do the seeds 
and similar parts of many plants move about in an extremely 
vigorous manner, but many undoubted Protophytes do so 
likewise. Motion is not and cannot at the present day be 
considered as indicative of aught else but change, physieal 
or chemical, else might a grain of gum-camphor darting 
about upon the surface of a glass of water, be classed among 
Vital organisms. 
E Doubtless many persons who see the question placed at 
E the head of this article have noticed some bright pool of 
1 fresh water, by the road-side or in a field, upon a spring or 
a summer’s day, and observed that it was either filled with 
^ seemingly gelatinous mass of light green matter, or had 
patches of darker green floating upon its surface. This was 
àn indication that Protophytes or simple plants were present, 
and, although there are chances that such an accumulation or 
Vegetation contains, or even entirely consists of, other organ- 
_ isms, yet in a number of cases hardly anything but Déimids 
Will be there found. To collect these little wonders we have 
Various methods suited to their mode of occurrence, and it 
Will be well to indicate them. ; 
First, then, they are inhabitants of fresh water, and in fact 
of the freshest kind of water only, decaying animal matter 
which would cause the water to become foul, even in a very 
ht degree, being sufficient to kill these tender plants and 
cause them to be replaced by forms of much greater sim- 
puc Seo jeune y brackish and marine — ; which were a 5 











