PROPERTIES OF VEGETABLE PROTOPLASM 358 
changes in its surroundings, and is capable of adapt- 
ing itself in various ways to such changed conditions. 
In many cases the adaptation in question takes the form 
of a spontaneous movement, in which the living substance 
is concerned in a manner which seems to resemble the 
behaviour of animal protoplasm. In others the response 
to such changes presents itself to us as a modification of 
the normal behaviour of the living substance with regard 
to the vital processes we have examined, and in particular 
to the entry of water into the vacuoles of the cells or its 
transmission outwards. 
When we examine the phenomena of movement we 
find that though evidence of contractility is procurable, 
this phenomenon is of somewhat rare occurrence in plants. 
Certain plants at particular times 
emit from their body small masses of 
naked protoplasm which are furnished 
with a varying number of long fila- 
ments (fig. 147). These filaments, 
which are protoplasmic also, are 
ordinarily in a state of active vibra- 
tion, causing currents in the water 
in which they live, which float them 
quickly from place to place. Among these free-swimming 
protoplasts may be mentioned the zoospores of the Algew 
and Fungi, and the antherozoids of these and higher plants. 
The movement is a spontaneous one, the organisms being 
endowed with the property of locomotion, which they exer- 
cise.in the discharge of their ordinary life-work. Though 
put forth in the absence of any external stimulation, the 
protoplasts are capable of receiving such impulses and 
modifying the vibratile action accordingly. 
The mechanism of the movement is probably the con- 
traction of each side of the filament or ciliwm alternately, 
or of the part of the cell just at the point of attachment. 
The impulse leading to the movement must be sought in 
some decomposition originating in the protoplasm itself, 
28 
Fie. 147.— Zoospore or 
Ulothriz. x 600. 
