54 
stamen— the antlierozoid to a pollen grain — the archegoniuin to a 
pollen tube, and the germ to the ovule. 
Before quitting the non-silicious algae, I must allude to the 
desmidim. The members of this family bear a great superficial 
resemblance to the diatomacese, but if carefully studied, important 
disthictions may he detected. The desmids do not secrete silex ; 
self-division takes place longitudinally in diatoms, transversely in 
desmids. Diatoms are found in equal abundance in fresh and 
salt water — desmids in fresh water only. 
The desmids resemble diatoms in being unicellular, rarely form- 
ing permanent filaments, the non-filamentous forms varying greatly 
in contour surface of cells sculptured. The commonest form of 
desmid belongs to the genus closterium, and resembles a cucumber 
in miniature. Species of this genus, particularly C-lunula, may be 
found in every ditch or bog pool. In this species the interesting 
phenomena of cyclosis or circulation may he easily observed : at 
the apices of the frustule are two transparent spaces, within these 
minute granules will be seen circulating, and if attentively ob- 
served, this circulation may be detected over the whole internal 
surface. A slight jirogressive movement has been seen in some of 
the fusiform species, but it is always very languid. The colouring 
matter (endochrome) in the desmids appears to he the same as the 
chlorophyl in the larger plants, and on examination by the spectro- 
scope, the absorption band peculiar to the latter material makes 
its appearance. 
The reproductive power lies in the endochrome, and certain 
changes take place in it previous to the separation of the frustule, 
and the formation of the sporangium. The external waU of the 
cell IS tenacious, flexible, and not easily ruptured. Mr. Ealfs says 
that silica is sometimes present, but I have never been able to 
detect its presence. 
Increase by self- division takes place in the desmidiaj; the 
frustule separates transversely, and a new half is gradually pro- 
duced. In^ Micrasterias this first appears like a little knob or 
button, this, in course of a few hours, increases in size, and deep 
indentations make their appearance, and the new half soon becomes 
a fac-simile of the older portion. 
Eeproduction in the desmidim takes place in the following 
manner. "VV hen two frustules are in proximity, they mutually 
