The Life of the Plant. | 199 
explained by the continual interchange, through the medium of the 
stomata, of the gases formed in the intercellular spaces with the external 
air, and by the fact that in growing plants gases are continually passing 
in and out of the cells by the force of diffusion. A large number of 
very remarkable movements of plants and of parts of plants are at least 
to some extent explained by the co-operation of these forces; but a 
large number of others still require further investigation. 
The wonderful properties of protoplasm, to which atten- 
tion has already been directed, culminate in its spontaneous 
motility, in its capacity of assuming different forms, of 
changing its outline and its internal condition, and of thus 
calling into activity internal forces without any correspond- 
ing impulses being observed to act upon it from without. 
Good examples of this capacity are afforded by hair-like 
structures, such as the filaments of the stamens of Z7ades- 
canta, the stinging-hairs of the nettle, &c. ‘The movement 
of the protoplasm in these cells is apparently not subject to 
any definite law, sometimes advancing, sometimes retreat- 
ing, and sometimes suddenly ceasing. The protoplasm 
often makes for itself new courses in the cell-sap; but its 
motion appears to be dependent on the nucleus, round which 
it always flows, and often carries it along with it. When 
the protoplasm within a cell possesses this power of motility, 
it is not extraordinary that cells destitute of a cell-wall (pri- 
mordial cells) should have the power of moving from place 
to place ; and, in fact, the naked primordial cells of the 
Myxomycetes, which are termed /lasmodia, are endowed 
with the faculty of moving like an animal, and even, in the 
case of Athalium—the so-called ‘flowers of tan’—of creeping 
to the distance or height of several feet, as if endowed with 
voluntary power. It 1s, therefore, not to be wondered at 
that even till quite recently these organisms were considered 
to be animals; while at present they are assigned to an 
abnormal section of Fungi, to which class they are allied by 
the mode of formation of their spores. The rapidity of these 
‘ streaming ’ movements varies greatly ; the maximum appears 
