No. 461.] MOVEMENTS OF DIATOMS. 289 
Streams of oxygen may be readily seen evolving from all parts 
of many of the larger aquatic plants when submerged in water 
and exposed to strong light, but in the diatom while the gas pro- 
duced is large in amount compared with the size of the organism, 
the actual amount evolved is so small that it is taken into solu- 
tion almost immediately. That such evolution takes place, how- 
ever, is shown by Professor Smith’s experiments with indigo. 
If now we examine the artificial diatom made of aluminum and 
placed in strong caustic solution we find that the bubbles from 
all sides come together and rise in a line corresponding to the 
median line or raphe of the organism, and that if indigo is placed 
in the liquid it collects and rotates near the central nodule just 
as described by Professor Smith to prove his theory of the pres- 
ence of water currents. 
It is therefore evident that the motion of diatoms is caused by 
the impelling force of the bubbles of oxygen evolved, and that 
the direction of the movement is due to the relatively larger 
amount of oxygen set free first from the forward and then from 
the rear half of the organism. This accounts for the hesitancy 
and irregular movements as well as the motion forward and back- 
ward over the same course. 
The evolving gas seems to act at times as a propeller to push 
the organism forward and at other times to exert a pulling action 
to raise the growth on end. The various movements described 
are the resultants of varying proportions of both of these active 
forces. 
The fact that a longitudinal groove on the under side of the 
artificial diatom causes it to become more active, due to the 
expulsion of the gas along the line of the groove, explains the 
greater activity of the Raphideze. 
The most interesting and peculiar movements among diatoms 
are those of Baci/laria paradoxa whose frustules slide over each 
other in a longitudinal direction until they are all but detached 
and then stop, reverse their motion and slide back again in the 
opposite direction until they are again almost separated. When 
the diatoms are active, these alternating movements take place 
with very considerable regularity. It is probable that the indi- 
viduals in a group of Bacillaria are joined together much more 
