290 THE AMERICAN NATURALIST. (VoL. XXXIX. 
loosely than other laterally attached genera and that when a 
forward movement takes place in the outer individual it is 
arrested by capillarity just before the diatom is completely 
detached. 
It can now be readily seen that the strange movements of 
the other microscopic plants may be explained as also due to 
the evolution of oxygen gas. While the movements of desmids 
are not as strongly marked as those of diatoms, many of them, 
notably Penium and Closterium, have often been described as 
having a power of independent motion, and Stahl! found that 
this motion is greatly affected by light. 
The best account of the movements of desmids has been 
given by Klebs? This author speaks of four kinds of move- 
ments in desmids, viz. : — 
(1) A forward motion on the surface, one end of each cell 
touching the bottom, while the other end is more or less ele- 
vated and oscillates backwards and forwards. ae 
(2) An elevation in a vertical direction from the substratum, 
the free end making wide circular movéments. 
(3) A similar motion, followed by an alternate sinking of the 
free end and elevation of the other end. 
(4) An oblique elevation, so that both ends touch the bot- 
tom — lateral movements in this position; then an elevation 
and circular motion of one end, and a sinking again to an 
oblique or horizontal position. 
This observer considered these movements to be due to an 
exudation of mucilage, and the first two to the formation, dur- 
ing the action, of a filament of mucilage by which the desmid 
IS temporarily attached to thé bottom and which gradually 
lengthens. 
These four kinds of movements are very easily explained by 
the theory of the evolution of gas, and by regulating the condi- 
tons they can be exactly reproduced in the artificial desmids 
made of aluminum. In this case strips of thin aluminum foil 
should be used. When the gas production is very strong at one 
; Verhandl. Phys. med. Gesellsch. Würzburg, 1880, p. 24. 
Biol. Centralblatt, 188 5, P. 353. 
