180 Clifford. — Notes on some Physiological 
elapses before spreading begins. The plasmodium will live 
for an indefinite period, several months at least, if kept 
sufficiently moist and clean. But if fresh water is not 
frequently supplied, and the substratum changed, it soon 
spoils, a certain disagreeable odour and a reddish-brown 
colour being an indication that this condition is coming on. 
There is now (July i) in the laboratory plasmodium which 
has been spreading since the 5th of January last. For the 
past three months no food has been given it but water, and 
it has no doubt been nourished by the microscopic Fungi 
and Algae growing in the rotten wood upon which the plas- 
modium has been kept. 
Rheotropism. 
Concerning rheotropism of plasmodia, the only original 
work thus far published is that of Strasburger, Jonsson, and 
Stahl. In 1878, Strasburger 1 discovered that plasmodium 
will move against a current of water in the substratum. 
In 1883, Jonsson 2 observed this property, and gave it the 
name of positive rheotropism, and in the following year 
Stahl 3 corroborated Jonsson’s work and adopted his term. 
But in none of this work was there an attempt to measure 
the force of the current against which the plasmodium will 
move, or to eliminate the possibility of the movement being 
induced by a search after food contained in the water. 
A series of carefully repeated experiments have proven 
that the plasmodium employed in this study will, when kept 
at a uniform temperature and removed from the influence 
of light, constantly advance against a current of distilled 
water ; and furthermore, if two currents, one of distilled and 
one of hydrant-water, are caused to flow against it, the 
substance will as often flow against the one as the other. 
1 Strasburger, Wirkung des Lichtes und Warme auf die Schwarmsporen, p. 71, 
Jena, 1878. 
2 Der richtende Einfluss stromenden Wassers auf wachsende Pflanzen und 
Pflanzentheile (Rheotropismus), Ber. der deutsch. bot Ges., Bd. 1, p. 512, 1883. 
3 Zur Biologie der Myxomyceten, Bot. Ztg., p. 144, 1884. 
